How to install a bottom drain for the basin?

How do you install a pond bottom drain? How do you install a bottom drain? How do you set a bottom drain? Many of you ask us if a bottom drain is mandatory in a pond.

It all depends on whether your installation is pump-fed or gravity-fed. We also recommend them for pressurized installations, such as swimming pools.

• Gravity installation (gravity-fed filtration)
• Pressurized installation (e.g., shark-bead - econobead)

A swimming pool drain can be compared to that of a bathtub. In a pond, when well-optimized, it allows for more possibilities than your bath :) Once the bottom drain is installed, the drain hole is protected by a protective grate to prevent fish from passing through.

Is a bottom drain mandatory in a pond?

This is often one of the regrets of our pond owners who have a gravity-fed installation (see below).

Pump-fed installation:

Installation for a bottom drain:

A bottom drain is a bit like a drain in a sink. It allows waste on the bottom to be evacuated. Traditionally, bottom drains were primarily used in swimming pools.

Many pond enthusiasts have to clean their ponds in the spring and autumn, and these drains, when combined with a good pump + a pre-filter, make their job much easier. It removes debris from the pond bottom drain to the filters, where it can then be removed.

Why install a bottom drain?

A bottom drain is a drain connected to the pond filter. Dirt sediment on the bottom is thus removed and transported directly through the drain.

When installing a pond, the drain must be placed at the deepest point of the pond. Especially in the case of koi ponds, this is an effective method for removing waste and moving it up to a sieve filter or any other filtration solution. Bottom sludge is disastrous for clear water and a pathogen for your fish (bacteria).

Here is an example of the pond principle with a bottom drain (pressurized):

Here is an example of the pond principle with a bottom drain (gravity-fed):

Bottom drains use a mechanism called "gravity flow." Due to water pressure, the water containing dirt will flow on its own through the drain into the multi-chamber filter.

The pump will be in a dry position, after the filter, to send the filtered water back to the pond. By using a drain, the filter will always be full of water, even in the event of a power outage.

Which bottom drains should I choose for my pond?

For a pond installation with gravity-fed filtration, we recommend working with 110 mm pipes. This will allow for the maximum amount of water to enter your filtration system.

It is also an excellent solution should you ever need to unclog a drain. Also, prioritize the use of 45° elbows.

For a pressurized installation, there are different calculation methods to determine the optimal section to use. Most of the time, we work with 63 mm sections, like those you can find by clicking here.

Where should you install a bottom drain? We recommend installing a bottom drain in a sump area. It is often a location where waste evacuation will be optimal.

The bottom drain is a part to be sealed, just like the skimmer or returns in a natural pool. It is often complicated, or even impossible, to do it later without undertaking major work.

Different types of bottom drains

• Bottom drains to be placed on the bottom
• Bottom drains to be placed laterally
• Inverted bottom drains

For the majority of fish ponds, a reinforced 110 mm drain to be placed on the bottom is the most common choice. If you raise koi carp, a drain equipped with an aeration cap also helps to oxygenate the water from the bottom.

In a masonry or poured concrete pond, the drain is cast directly into the slab. Choose a model designed to be set in concrete, with its protective grille.

G-MOD 1466 concrete bottom drainDrain with grille, to be cast into the floor of a concrete pond.View product

How do you place the bottom drain?

We recommend placing the bottom drain at the deepest point of the pond. It is generally placed in a sloped area. You can place it at the bottom of the pond or at the foot of the wall of the deepest area.

When you install a bottom drain, before pouring the concrete, we recommend filling the pipes with water. It is common for pipes to float up during the concrete pouring if they are filled with air.

You can also call upon our network of certified professionals by contacting our team via support@foudebassin.com. We will be happy to recommend a professional in your area.

Gravity-fed or pump-fed: the two setups

The bottom drain does not function in the same way depending on the type of filtration. In a gravity-fed system, the water flows on its own from the drain to the filter because the filter is installed at the pond's water level: this is the principle of communicating vessels. In a pump-fed or pressurized system, it is the pump that sucks the water through the drain before sending it into the filter.

Gravity-fed requires more work (filter buried at water level, large-diameter pipes), but it protects the pump from waste and allows for treating large volumes. Discover our gravity-fed pond filters. To design the entire pond, our article on how to make a fish pond details choices regarding volume, depth, and filtration.

Installing a bottom drain step by step

The drain is placed during construction, before the pond liner or concrete. Here is the most common sequence of operations; always follow the manufacturer's instructions for your drain regarding the sealing connection.

1. Locate the low point. Form a slight sump at the deepest point, with a slope from the bottom towards the drain so that sludge converges there.
2. Dig the pipe trench. Trace the most direct path possible to the filter, under the pond floor, limiting the number of elbows.
3. Assemble the drain and pipe. Glue the PVC fittings after cleaning the surfaces with a suitable cleaner. Prefer 45° elbows over 90° elbows.
4. Prop and weight down. Fill the pipes with water before pouring the concrete to prevent them from rising.
5. Connect the waterproofing. Fix the liner or tarp to the drain using the provided flange and seals, without any folds at the tightening point.
6. Test before backfilling. Fill with water and check for leaks at the drain and connections.

Complete this with our PVC parts (elbows, sleeves, fittings) and our PVC glues and cleaners. To absorb small offsets between the pipes and the filter, flexible fittings are very practical.

Connecting the drain to an EPDM liner

It is one of the most frequent questions: how do you fit a bottom drain in an EPDM-lined pond? The principle is the same for all flanged drains. The liner is laid over the drain, then sandwiched between the drain body and a screwed counter-flange, with the seals supplied.

1. Lay the liner flat over the drain, with no fold where it will be clamped.
2. Fit the seals and the counter-flange, then tighten gradually in a cross pattern to spread the pressure.
3. Cut the liner inside the flange only once tightening is complete.
4. Put a little water in the pond and check for leaks around the flange before carrying on.

The same principle applies to wall passages, which let a pipe pass through the liner, for example to a skimmer or a filter return.

Valve, skimmer, wall passage: completing the installation

A bottom drain removes waste from the floor, but it does not work alone. Three elements complete it in a well-designed installation.

• A valve on the drain pipe, on the filter side: it isolates the drain so you can clean or work on the filter without emptying the pond. 110 mm slide valves are the most widely used.
• A skimmer for the surface: the drain draws from the bottom, the skimmer collects leaves and floating debris before they sink.
• Wall passages to run pipes neatly through the liner.

Reinforced 110 mm bottom drainOur best-selling model, with protective cap.View product110 mm drain + aeration domeSludge suction and aeration from the bottom.View productDN 110 PVC slide valveTo isolate the drain when working on the filter.View product110 mm screw-on liner passageExtra-strong wall passage to go through the liner.View productFloating skimmer, 110 mm connectionCollects surface debris, alongside the drain.View product

Errors to avoid

• Placing the drain somewhere other than the lowest point: sludge then accumulates next to it.
• Multiplying 90° elbows: they slow down the flow and clog more easily.
• Under-sizing the pipe in gravity-fed systems: the filter does not receive enough water.
• Pouring concrete with empty pipes: they may rise during the pouring process.
• Forgetting to provide a valve to isolate the drain during filter maintenance.
• Backfilling before testing for leaks.

Frequently asked questions