Soakaway not draining: signs, causes and what fixes it

What a soakaway is and where to find yours

A soakaway takes surface water only: rain from roofs, downpipes, driveways and patios. It is not meant for sink, toilet or washing machine waste, which should go to the foul drain. Older soakaways are usually a hole filled with rubble or hardcore. Newer ones are plastic crates wrapped in a fabric membrane, or a perforated concrete ring chamber, often with an inspection chamber on the pipe just before it.

Many London houses have no soakaway at all, because their rainwater runs into the public sewer. Soakaways are more common in outer boroughs, on newer extensions and on houses that were not allowed to connect rainwater to the sewer. To find yours, follow a downpipe that does not end at a gully connected to the house drains, look for a manhole cover somewhere in the garden that nothing else explains, and check your property's drainage plan or survey. Approved Document H advises that a soakaway should normally sit at least 5 metres from a building, so it is often at the far end of the garden.

Signs a soakaway is blocked or failing

Soakaway problems show up when it rains, then fade as the weather dries. That pattern is the clue: if a downpipe or gully only overflows in heavy rain and is fine the rest of the week, the water has nowhere to go at the far end of the pipe.

• Downpipes spurting at the joints or gullies overflowing during rain
• A wet, spongy or sunken area of lawn above or near the soakaway
• Standing water in the inspection chamber a day or more after rain
• Water pooling against the house wall or along a path after storms
• Gutters overflowing even though they are clear of leaves
• Damp patches on internal walls near a downpipe that backs up

Rainwater backing up against a wall, an airbrick or a basement can soak into the building. If water is pooling against the house, divert the downpipe away from the wall with a length of pipe or a hose until the drain is sorted.

Blocked pipe or failed soakaway: how to tell the difference

The fix depends on where the water is stopping, so it is worth a few minutes with a torch before calling anyone. Lift the inspection chamber cover nearest the soakaway, if there is one, after a spell of rain.

If the chamber is empty but the downpipe still backs up, the blockage is in the pipe between the house and that chamber. If the chamber is full, water is not getting away into the soakaway, which means either the last length of pipe is blocked or the soakaway itself has stopped taking water. A soakaway that fills and then empties very slowly over a day or two is usually silted up or sitting in ground that no longer drains.

Why soakaways stop draining

Silt is the main reason. Every storm washes grit from roof tiles, moss, leaves and fine soil into the pipe, and over years it settles in the bottom of the pit and clogs the gaps in the rubble or the membrane around the crates. Rubble soakaways have no way of being cleaned, so once they silt up they usually have to be dug out.

Ground conditions matter just as much. Much of London sits on London Clay, which lets water through very slowly. A soakaway dug into clay may cope with light rain but fill and stay full after a wet week, and it will get worse in winter when the ground is already saturated. A soakaway can also fail because tree roots have grown into it or into the pipe, because the pipe has cracked or sagged, or because more roof or paving now drains to it than it was built for, for example after an extension or a new driveway.

What you can safely do yourself

Start at the top. Clear gutters and gully grids of leaves and moss, and scoop out the silt from the bottom of any gully trap. Run a hose into the gully and watch the inspection chamber to see whether the water arrives and how quickly it leaves. If you have drain rods, you can rod the pipe from a gully or chamber towards the soakaway, turning the rods clockwise only so the joints do not unscrew.

Do not pour drain chemicals into a soakaway. They do nothing to silt or clay and end up in the ground. Do not try to dig out a soakaway yourself either: the pits are often deep, the sides can collapse, and there may be cables or other pipes nearby. If you are unsure whether the drain carries only rainwater, our blocked outside drain guide explains how to read the chambers on a foul drain.

How a drainage engineer investigates and repairs it

An engineer will first clear the pipe feeding the soakaway, usually with rods or a jetter, and then put a camera down it. A CCTV drain survey shows whether the pipe is blocked, cracked, displaced or full of roots, and how far it runs before it reaches the soakaway. Our drain cleaning methods compared guide explains when rods, jetting or root cutting are used.

If the pipe is clear and the soakaway still will not drain, the options depend on how it was built. A crate or chamber soakaway with an access point can sometimes be jetted and desilted. A rubble soakaway that has silted up usually has to be excavated and rebuilt, and a new one is normally sized from a percolation test that measures how quickly water drains from a trial hole, following the BRE Digest 365 method. On heavy clay, the answer may be a larger soakaway, rainwater storage, or permission from the water company to connect to a surface water sewer instead. Our guide on when drain excavation is needed covers what digging involves.

Who is responsible for a soakaway?

A soakaway on your land that takes water only from your property is yours to maintain and repair. The 2011 transfer of private sewers to the water companies covered pipes that connect to the public sewer, so drains that run to a soakaway, even when they are shared with neighbours, generally remain private. If a soakaway serves several houses, the owners usually share the cost of fixing it, and your deeds or the original planning documents may say how.

You cannot simply reconnect a failed soakaway to the public sewer. Connecting to a public sewer needs the sewerage company's consent, which in most of London means Thames Water, and new rainwater connections to foul or combined sewers are discouraged. Our shared drain and sewer responsibility guide covers the wider rules. If you rent, report a failing soakaway to your landlord, and if you are buying, ask the seller how rainwater drains before exchange.

When a soakaway problem needs urgent help

A slow soakaway in summer can wait for a planned visit. It becomes urgent when rainwater is pooling against the house, coming in through an airbrick, a door threshold or a basement, or when the backed-up drain turns out to be carrying foul water as well, which points to a misconnection or a blockage in the house drains rather than the soakaway.

Loyal Plumbers clears and investigates drains across London and everywhere inside the M25, with 10 vans working 24 hours a day. Call 020 4652 8585 or send an enquiry and tell us which downpipes or gullies back up, whether the inspection chamber is full and whether there has been any building work nearby. Our call-out charge is £60, and the engineer explains what clearing or surveying the drain will involve before starting.