How do I connect a downpipe into a drain?

Shoe, gully or direct connection — which is right, and how to make the connection so it does not block, smell or discharge to the wrong place.

Difficulty: intermediate
Time: 3 hr
Read: 4 min
Safety: caution

Short answer

Establish whether the drain is surface water or combined first. Then use a shoe discharging over a trapped gully, or a back-inlet gully with a sealed connection, or a direct connection into a rainwater-only system with an access point above ground.

A downpipe has to get water into the ground drainage without blocking, without smelling and without letting the whole system back up into your gutter. Which arrangement is right depends on what kind of drain is underneath.

Safety

Rainwater must not be connected into a foul drain, and foul water must never go into a surface water drain — both are offences and cause pollution or flooding. If you cannot establish which drain you have, ask your water company or a drainage contractor. Wear gloves when working in a gully and wash thoroughly afterwards.

Step by step

Find out what the drain is.Surface water drains take rainwater only and usually discharge to a watercourse or soakaway. Foul drains take waste. Combined systems take both. Lift the covers, look at what runs into each, and check with the water company if it is unclear.
Never connect rainwater into a foul-only drain.It overloads the sewer and causes flooding and pollution downstream. It is also an offence. Where there is genuinely no surface water drain, a soakaway is the usual answer.
Choose the connection type.A shoe discharging over an open trapped gully is simplest and easiest to maintain. A back-inlet gully takes the pipe in below the grating and stops leaves getting into the gully. A sealed direct connection is neatest but gives no access for clearing.
Keep a trap between the pipe and any combined drain.Anything connecting to a combined or foul system must go through a trap, or the smell comes back up the downpipe. A gully trap does this.
Set the shoe to discharge inside the grating.The bottom of the shoe should sit over the gully, discharging inside the grate rather than splashing on it. Water hitting the grating splashes the wall and stains it.
Fit a leaf guard at the top, not the bottom.A balloon guard in the downpipe outlet at gutter level catches leaves where you can reach them, rather than letting them jam in the gully or the underground pipe.
Support the downpipe properly.Pipe clips at no more than 1.8m centres and at every joint, screwed into the masonry rather than the mortar joints where possible. An unsupported downpipe pulls the shoe out of the gully.
Test the whole route.A hose into the gutter for several minutes. Watch the gully takes it without backing up, and check the downpipe joints for leaks under flow.
Keep the gully clear.Lift the grate and clear the silt trap a couple of times a year. A blocked gully backs up and floods the base of the wall, which is a damp problem waiting to happen.

Tips

A back-inlet gully is worth the extra work where leaves are a problem. It stops the gully filling with debris.
Photograph and sketch the drain runs when the covers are up. It is very useful information to have later.
Where a downpipe discharges onto a hard surface rather than a drain, a rainwater diverter to a water butt with an overflow to a soakaway is often a better solution than a new connection.

Common mistakes

Connecting a downpipe directly into a foul drain — Rainwater overloads the foul sewer, causing flooding and pollution. It is an offence and the water company can require it to be disconnected at your cost.
Sealing a downpipe directly into an underground pipe with no access — When it blocks — and it will — there is no way to rod it. Always leave a rodding point or discharge over an accessible gully.

If it doesn't work

Gully overflowing in heavy rain

Cause: Silt trap full, or the underground pipe partially blocked — Fix: Clear the gully trap first, then rod the run from the nearest inspection chamber.

Smell coming from the downpipe

Cause: Connected to a foul or combined drain without a trap — Fix: Discharge over a trapped gully, or fit a trapped back-inlet gully. Never connect untrapped to a foul system.

Water splashing the wall at the base of the downpipe

Cause: Shoe discharging onto the grating rather than into it — Fix: Extend or reposition the shoe so it discharges inside the gully. Wall staining and damp at low level follow otherwise.

Downpipe pulling away from the wall

Cause: Too few clips, or clips fixed into mortar joints — Fix: Add clips at 1.8m maximum centres and fix into the brick rather than the perp joints.

Questions people ask

Can I connect my downpipe to a soakaway?

Yes, and it is often the right answer where there is no surface water drain. The soakaway must be at least 5m from any building and sized for the roof area and the local soil infiltration rate.

How do I tell if a drain is surface water or foul?

Lift the cover and look. A surface water drain is clean, takes only rainwater, and often has no trap. A foul drain will have waste appliances connected. If you cannot tell, the water company holds sewer records and can advise.