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Dormer Cottage, Spurgrove Lane, Little Frieth,

Nr. Henley on Thames, Bucks, RG9 6NU

Phone/Fax: 01494 882600

Order Hotline: 07814 011357

Pond plumbing, drains, valves and fittings

At Koi Water Garden, we are able to offer competitive prices on not only high quality koi, but also on koi related goods such as all necessary pipe work and fittings.


last updated 10th April 2017


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Top tips for plumbing your pond.


Pond plumbing may seem like a complete mystery to many, who quite understandably tend to think of plumbing in a Koi pond in a similar way to plumbing in a house. There are however few similarities, not only with the materials and pumps used, but also in the level of complexity. Pond plumbing need not, and indeed should not be complex. there are two basic plumbing systems – one for gravity filter installations and one for pump fed.


Pumped filters.


In pump fed installations the filter pump is operating in the pond and this is normally connected to the filter inlet with flexible piping. The UV unit should be installed between pump and the filter inlet and any heater or heat exchanger fitted should also be fitted in the same position either directly before, or after, the UV and before the filter inlet.


Always fit a suitable slide or ball valve immediately before the filter inlet so that the pond and filter can be separated and water kept in the filter with the pump switched off.  Input pipe work from pump to filter which is under pressure should be minimum 1.5” to avoid unnecessary flow losses.


Remember to keep pipe runs as short as possible with as few bends as possible and also remember to trim any universal hose tails fitted (often supplied with pumps and Uvs) to the maximum diameter possible – again to avoid flow restrictions.


Insufficient pipe diameters and too many restrictions can reduce the rated pump output by over 50% and put back pressure on the pump leading to premature failures.

With pumped installations, the filter must be above the water level in the pond so that water can be returned to the pond by gravity.


On the return side of the filter, one would normally use a minimum of 2” pipe work to return water to the pond. Because the water return operates under gravity a bigger pipe diameter will be needed to cope with the pump flow. Also the longer the return pipe work, the larger the diameter the pipe needs to be, so we would normally recommend a practical minimum pipe size of 3” for pumped filter returns. It is also normally simpler to step up a pipe size rather than using multiple smaller pipe returns. A single 3” pipe has a larger bore area than 2 x 2” pipes and a single 4” pipe has a larger bore area than a two 3” pipes. So in this respect at least size matters!


Gravity filters.


With gravity installations, the water level in the filter is the same as the water level in the pond, so gravity filters normally reside in purpose made filter chambers which are excavated at the same time as the pond in order to simplify construction.


In gravity installations, the filter input is fed by pressure of gravity, which forces water through a large (normally 4”) pipe buried in the floor of the pond or fitted low in a side wall and into the filter.

 A 4” diameter pipe is chosen since water flow through it is slow, and solids carried into the filter arrive intact, this means the filter can cope with these solids more efficiently, and remove them more easily.


The 4” pipe is normally connected in the pond to a large sump type bottom drain which when installed allows water ingress via a small peripheral gap which prevents fish from entering the pipe work, but allows all the unwanted solids to pass. The connecting 4” pipe is run horizontally in the ground or concrete slab under the pond and then exits vertically into the filter chamber in a suitable position ready to connect to the filter inlet. Always fit a suitable slide or ball valve immediately before the filter to separate pond from filter for cleaning and purging purposes.


On the return side of the filter, water is drawn from the filter by a suitable pump, which should always be mounted below water level and which is then connected to a suitable UV (and heater or heat exchanger if fitted), and then to pipe returns normally fitted into the pond walls. The return pipe work is normally 1.5” with a gravity installation, as here the returned water is under pressure. Again never use pipe work less than 1.5” in diameter, and if pipe runs are very long, step up the pipe diameter to 2” to avoid frictional flow losses in the pipes. Similarly avoid too many sharp bends in return pipe work, and use swept bends wherever possible. Always fit a suitable slide or ball valve immediately after the filter, and before the pump in order to separate pond and filter to allow for maintenance of pumps and UV and to allow for cleaning of the filter.


It is always a good idea to use at least two pond returns, located at opposite corners of the pond, which will help to maintain a circular flow, even in square or rectangular ponds, and this helps to "wash" the floor of the pond and encourages dirt to move to the centre of the pond base where the bottom drain should be located.


With two (or more) returns operated from one pump, remember that balancing valves should be fitted to the shortest return pipe runs so that the flows through all of the return pipes can be equalised. If these are not fitted, most of the pumped water returning to the pond will exit the shortest pipes only as it will follow the path of least resistance.


Top Tips for Pond Plumbing.


  • Never put installed pipe work under stress – there is limited pressure in Koi pond installations, but long unsupported pipe runs full of water and pipes forced into positions they don’t really want to be in are asking for trouble.
  • Always used solid glued pipe work wherever possible, and NEVER use ANY push fit components.
  • Always fit pipe runs dry first and mark joints and angles with a felt pen so that they can be removed and then glued in the correct position.
  • Always glue the shortest pipe runs first – you will have more flexibility to move, remove and refit long pipe runs more easily because the long pipe will flex and allow more movement.
  • Always use ball valves in any pipe work to control flows.
  • Always use slide valves as waste or stop valve only so that when in use they are shut.
  • Preferably always mount them in vertical pipe runs.
  • Never use slide valves in a horizontal pipe run so that they are open when in use, they will fail within months as the shutter grooves fill with dirt and prevent the shutter from closing properly.
  • Always use a minimum of 1.5” pipe work for pipe runs under pressure and minimum 3” for gravity flow pipe work.
  • Increase pipe diameters as pipe runs becomes longer.
  • Always use swept bends rather than knuckle bends wherever possible.
  • Always use pressure pipe for buried pipe runs and bed such pipe runs in sharp sand or pea shingle to allow for movement.
  • Similarly always use pressure pipe for any pipe runs that are exposed and liable to be stepped on, kicked or are otherwise vulnerable to damage.
  • When plumbing waste pipe work from filter/vortex drains, always step up fitted pipe sizes to a minimum of 2” to avoid any possibility of the pipes becoming clogged with weed and/or leaves and other detritus. Always use swept bends in waste pipe work.
  • Always install Pumps, Uvs, Heaters etc using demountable single union connectors so that all components can simply be removed for maintenance.
  • Always install valves immediately before and after filters (gravity installations) and near pond returns so that all elements of the filter system can be removed without water being drained from the pond or filter.
  • In pumped systems always use reinforced flexible piping from the pump and NEVER sit the pump on the pond floor – always at least 12” above the base of the pond. In this way should there be a disaster, the pond can never be completely emptied and the fish will be safe.
  • It is good practice to use a dedicated pump for the filter flow, and to use separate pumps for other water features such as waterfalls and skimmers, which may need to be switched on and off, or may operate with variable water flows.





Valterra Slide Valves

Valterra slide valves are tough and dependable - made to last! Designed to fit imperial PVC pressure pipe. Will fit solvent weld waste with suitable adaptors (see below). Mainly used for on/off waste valves in filters and to separate filter from pond, to completely shut off flow when required. Not suitable for flow restriction or control.

Size Price
1.5" £9.50
2" £13.95
3" £27.50
4" Steel shutter £44.50
Valterra slide valve

Double Union Ball Valves

Ball valves are ideal to restrict pipe flows, as purge valves and waste control valves. Easy to dismantle and maintain and very strong - fits standard imperial PVC pressure pipe. Will fit solvent waste with suitable adaptors (see below). Adjustable for pressure.

Size Price
3/4" £8.95
1" £10.95
1.5" £14.95
2" £22.95
3" £96.95
4" £115.95
Double Union Ball Valves

Pipe adaptors - Solvent waste to PVC pressure piping

Pipe adaptors enable the use of ball valves, slide valves and other fittings that are imperial (English) pipe sizes to fit metric waste pipe. Simply glue over the end of the solvent weld waste pipe before fitting to the appropriate valve or fitting. One required for each side of the valve.



Size Price
40mm - 1.5" £0.95
50mm - 2" £1.25
82mm - 3" £1.95
110mm - 4" £2.25
Pipe adaptor sleeves

Universal 2 inch to 1.5" converter fitting

This is a really simple and great idea - a fitting which can be used on 1.5", 40mm, 2" and 50mm pipe work, and can convert from solid piping to flexible all in one fitting. The rear end of the fitting, shown below left, features a 1.5" BSP female thread on the inner side and a 50mm solvent weld fitting on the outer. With the addition of a 50mm pipe adaptor, this solvent weld fitting is instantly converted to a 2" imperial fitting. The front end of the fitting , shown below right, will allow the connection of a 2" or 50mm flexible pipe on the outer connection or a 40mm solvent weld pipe fitting on the inside. Clever or what! 



Size Price
1.5 - 2 inch £4.95



In wall skimmer

In pond design with floating weir plate to prevent koi entering skimmer whilst chasing food. Also complete with catch basket and removable lid for easy cleaning. Will suit liner or concrete ponds - complete with rubber gaskets and screw in flange plate in order to fit to liners. When fitting to concrete block walls, standard skimmer replace 1/2 of a 450mm concrete block. The wide mouth skimmer replaces a complete block.


 Can be fitted to either solvent waste or PVC pressure pipe with relevant 1.5" male threaded fitting (not supplied).


skimmer guard plateAbove: - Skimmer guard Plate.

Size Price
Standard In wall skimmer approx 9" wide x 9" deep at face. £36.50
Wide mouth in wall skimmer. Complete with screw on wide angle mouth approx 15" wide at face x 9" deep. £49.50
Grid pattern skimmer guard. Replaces standard skimmer front plate - standard size £24.50
Grid pattern skimmer guard.Replaces wide mouth skimmer front plate - widemouth size £29.50
standard in wall skimmer

Above:- Standard In wall skimmer.


 wide mouth skimmer Above:-Wide mouth Skimmer - supplied in Black



Large sump bottom drain.

Features removable lid with screw on flange ring for fitting to liner or concrete ponds. 110mm version suitable for standard solvent weld waste pipe work and 4" for imperial PVC pressure pipe work.

Size Price
110mm Metric £19.50
4 Inch imperial £39.50
Large Sump Bottom Drain



Bottom drain converter socket

A special PVC pressure fitting that converts 110mm metric pipework to 4" imperial. The socket features 110mm for solvent weld waste pipe on one side and 4" socket to take pressure pipe on the other. Great idea and a very economical way of converting to pressure pipe sizes for bottom drain piping.

Size Price
110mm female/ 4 Inch female £17.50


Bottom Entry Side drain

Features removable lid with screw on flange ring for fitting to liner or concrete ponds. 110mm base entry pipe normally used when fitting drains in side walls of ponds. Can still be used mounted in pond base if required

Size Price
110mm side drain £19.50
Bottom Entry Side Drain



Spindrifter Aerated bottom drains.

Based on a 4" or 110mm large sump bottom drain, this aerated bottom drain has a 3/4" side entry for running airline into the drain via a separate pipe running alongside the main bottom drain pipe. (shown right) The Spindrifter aerated drain assembly incorporates a 10mm airline connector to feed air into the perforated drain lid in two parts - 1 part forming the lid itself, and the 2nd is a perforated disc which is built into the top of this lid (see far right).

The Spindrifter aerated dome assembly fits both 110mm and 4" bottom drains.

Specify 110mm size for solvent weld waste pipe and 4" size for imperial pressure piping.

Size Price
110mm Metric £119.00
4 Inch Imperial £134.00
Spindrifter drain converter £99.50
Aerated drain assembly 

spindrifter drain



Retro fit bottom drain cover assembly

A brilliant and simple idea to replace bottom drain covers (lids) that have either come off on their own or been removed, which are always very difficult to get back on once removed without going for a swim!

 These heavy duty drain covers are assembled with 3 stainless steel bolts and a heavy bottom ring.

 Just push into the bottom drain cavity with a net or similar to position, and can be lifted out easily with a net, for bottom drain cleaning.

 Fits all standard large sump bottom drains.



Size Price
110mm or 4 Inch £76.95
Retrofit Bottom drain lid




Non Return Valve

Provides a simple means of preventing backflow in pipe work where this would be undesirable as for example in pumped systems or where heaters are fitted in line and which must always be filled with water. Made of brass with 1.5" or 2" female threads. Fits any standard 1.5" or 2" bsp male screwed fittings

Size Price
1.5 inch £19.50
2 inch £27.50
Brass non return valve


Flow meters.

It can be extremely difficult to calculate flow rates for any system - final flow rates depend on many factors, pump power and design, siting, pipe sizes, number of bends and fittings used in plumbing, and the various equipment used with the water flow such as UVs, heaters etc. Measuring final flows is however very important, to ensure that you are turning over the pond water as appropriate - normally every 2 - 4 hours through your filter system.


So we are now able to offer an accurate flow meter at a very realistic price.


  • Direct Reading Scales
  • Impact-Resistant Machined Acrylic Body
  • Factory calibrated
  • Easy-to-Read Scales
  • Wear- and Corrosion-Resistant 316 SS Floats
  • Available to fit pipe sizes from 1.5 to 4"
  • Capacity:- 20 to 7200 litres/min


 flow meter for 1.5" pipe size.  £109.50
 Flow meter for 2" pipe size. £119.50
 Flow meter for 3" pipe size. £139.50
 Flow meter for 4" pipe size. £149.50




Metric waste pipwork

Please note that all pipe work can be supplied mail order - but carriage charges for 3m pipe lengths will be higher than those shown in the shopping cart as parcel lengths of over 2.5m are surcharged by all couriers - carriage will always be charged on 3m lengths of pipe work regardless of order value. We will confirm charges by return mail for each order placed. Alternatively ask to have your pipe lengths cut in half - that way normal carriage charges will apply. 

Type 40mm Buy 50mm Buy 82mm Buy 110mm Buy
pipe 3 metre length £9.50
straight connector £2.00
90 deg swept bend £2.00
45 deg bend £2.00
"T" connector £2.00

Heavy Duty Reinforced flexible piping.

Our reinforced flexible piping is a very strong, thick walled PVC based tubing that is reinforced for extra strength. Cannot be crushed and is very difficult to damage or distort. Designed to be mechanically fitted via an appropriate sized hosetail. Can also be solvent weld glued. Ideal where difficult, complex pipe runs are necessary. Will not split or go brittle with time.




Size Price
1.5 inch priced per metre £3.95
2 inch priced per metre £5.50
Heavy duty flexible pipe

Pressure Flexi - bondable flexible tubing

Pressure flexi is a very strong, thick walled PVC based tubing that is reinforced for extra strength. Cannot be crushed and is very difficult to damage or distort. Designed to be solvent welded into metric and imperial pressure pipe fittings and is therefore ideal where difficult, complex pipe runs are necessary. Ideal for underground as well as above ground applications. Will not split or go brittle with time.



Size Price
50mm Pipe per metre Metric/ imperial converter required for imperial pipe £4.95
63mm Pipe per metre. Metric/ imperial converter required for imperial pipe £5.95
50mm / 1.5" adaptor socket £2.75
63mm / 2" adaptor socket £3.75
Pressure Flexi bondable pipe

PVC flexible bend

A must for those tight and awkward plumbing jobs where the angles are never exact. This PVC flexible bend is solvent weld glued just like any other fitting but allows for movement in use and overcomes any jointing issues where the angles are not 45 or 90 deg. Note this is a metric fitting which can easily be adapted to 1.5" imperial pipe by using the 50mm - 1.5" shims supplied.



Size Price
50mm Flexible PVC bend £12.95
50mm - 1.5" shims (ea) £0.95
Flexible PVC bend

Solvent Weld Waste pipe Fittings

Male threaded connector

Above:- Male threaded solvent socket


Flanged Tank Connector

Above:- Flanged Tank Connector

Flanged Tank Connector

Above:- Screw type Tank Connector

Fitting type 40mm Buy 50mm Buy 82mm Buy 110mm Buy
Male threaded socket £1.95
Tank connector screw type £3.50
Tank / Liner connector flanged type £3.50

Other Solvent Weld Waste Fittings

Reducers and Hosetails

Fitting Type Price
Reducer 2 - 1.5" £1.95
Reducer 3 - 2" £3.95
Reducer 4 - 3" £4.95
Stepped hosetail - glued 3/4" to 1.5" £2.25
Stepped hosetail male threaded 3/4" to 1.5" £2.25

Above:- Stepped Hosetail - glue fit shown



Flexible Rubber Connectors


Rubber Fittings




These rubber connectors are the answer to many a Koi pond plumbing problem - where there are joints and angles that are not quite 90 deg or in line these fittings can be used as they are flexible and 'give' to allow strain free pipe joints. They are also ideal for use where both metric and imperial plumbing has been use as they will fit to either system. They are also convenient for any joints that need to be removed from time to time and don't need to be glued as a permanent fixture. Complete with terry clips that will tighten with a socket or spanner as well as a screwdriver for sure watertight joints. These joints are heavy duty and very thick walled and will not deteriorate with age.

Type 40mm - 1.5" Buy 50mm - 2" Buy 82mm - 3" Buy 110mm - 4" Buy
Rubber Socket £5.50
Rubber swept 90 deg Bend £8.75
Rubber "T" Joint £10.45

Rubber Reducers

These rubber connectors are the answer to many a Koi pond plumbing problem - simple reducers to bridge different pipe sizes without the need for glued joints and reducers - Very handy for both metric or imperial pipe sizes, will fit both standards

Size Price
2 - 1.5" £3.95
3 - 2" £8.95
4 - 3" £9.95
4 - 2" £9.95
6 - 4" £27.50
Rubber Reducers

Rubber End Caps

Handy to block up pipes either as a temporary or permanent measure - again fits equivalent metric or imperial pipe sizes.

Size Price
1.5" Rubber end cap £2.75
2" Rubber End cap £3.75
3" Rubber end cap £4.95
4" Rubber end cap £5.50
Rubber end caps




 PVC Pressure Pipe


PVC pressure pipe fittings 



PVC Pressure pipe is the standard for all Koi plumbing work. Supplied as class C D or E, pressure pipe is thick walled PVC and is very strong when compared to waste pipe work. It is recommended for all underground use and will withstand much higher pressures and stresses than normal waste pipe work. In particular it is recommended for all bottom drain pipework, or any pipework that is to be permanently buried in soil or under concrete.


Please note that all pipe work up to 3m lengths can be supplied mail order - but carriage charges for 3m pipe lengths will be higher than those shown in the shopping cart as parcel lengths of over 2.5m are surcharged by all couriers - carriage will always be charged on 3m lengths of pipe work regardless of order value. We will confirm charges by return mail for each order placed. Alternatively ask to have your pipe lengths cut in half - that way normal carriage charges will apply.


 ** We also supply pressure pipe in 6m lengths (see below), but these are only available for collection - we cannot ship these lengths by courier **.

Type 3/4 inch Buy 1 inch Buy 1.5 inch Buy 2 inch Buy 3 inch Buy 4 inch Buy
1 metre pipe length £3.65
3 metre pipe length £9.95
6 Metre pipe length **  £17.95 
straight connector £1.00
90 deg knuckle bend £1.75
45 deg bend £1.75
90 deg Swept bend  not available in 3/4 or 1 inch sizes £7.85
Equal "T" joint £1.85


PVC Pipe clip £1.35



PVC Pressure pipe - threaded sockets and unions


Male threaded pvc sockets

Above:- Male threaded socket


Female threaded pvc sockets

Above:- Female Threaded socket

Single union connectors 

Above:- Single union de-mountable connectors - 1 Male thread, 2 plain glued, 3 female thread. Fit to pumps and UVs for ease of removal. 

Type 3/4 inch Buy 1 inch Buy 1.5 inch Buy 2 inch Buy 3 inch Buy 4 inch Buy
Threaded female socket £2.75
Threaded Male Socket £1.75
Threaded Backnut £2.35
Female Threaded socket union £5.95
Plain socket union £5.65
Male Threaded socket union £6.95


PVC Reducers

Used to reduce pipe sizes from 4 inches right down to 3/4 inch if required. These are all gluable fittings, and are designed to fit into any standard pipe fitting of the larger size.

Size Price
Reducer 4 - 3" £8.95
Reducer 4 - 2" £8.95
Reducer 3 - 2 " £6.35
Reducer 2 - 1.5" £2.95
Reducer 1.5 - 3/4" £2.25
Reducer 1 - 3/4 " £1.65

PVC Reducers

Solvent weld cement

Tangit professional rapid cure solvent cement for solvent weld waste and all classes of PVC pressure and ABS waste piping. Cans complete with applicator brush. Tangit is by far the best solvent weld cement for professional use. Gap filling and slow grab allows time to move pipe joints once cemented. We suggest you use small cans (with small brushes) for 1.5 and 2" piping and large cans (with large brushes) for 3 and 4" piping.

Size Price
250ml Tangit £10.95
500ml Tangit £21.50

Pipe cleaner

Griffon professional pipe cleaner for solvent weld waste and all classes of PVC pressure and ABS waste piping. Cleans and de-greases pipe work in preparation for cementing. Ensures a complete and correct bond. Supplied in 500ml cans.

Size Price
500ml Griffon Pipe cleaner £12.95

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