Outside Drain Blocked or Manhole Overflowing: What to Do First

Stop the water going in, and why it matters

A blocked underground drain has nowhere to send what you pour into it, so the waste comes back out at the lowest opening on that run. In a house that is usually the manhole cover in the garden, a gully by the back door, a ground-floor shower tray or the downstairs toilet. Every litre you use upstairs ends up at one of those points, so the first job is to stop adding to it.

• Tell everyone in the house not to flush, shower, run a bath or empty a basin until you know where the blockage is
• Stop the washing machine and dishwasher. If one is mid-cycle, cancel it before the next pump-out; one pump-out is enough to push a nearly full chamber over the top
• In a house split into flats, knock on the other doors. Their waste may join yours before the chamber that is overflowing, and they will not know
• Leave rainwater alone. A downpipe that empties into the same gully cannot be switched off, so if it is raining, expect the level to rise and plan to protect doorways with towels or a board

If dirty water is coming up inside, keep children and pets out of that room and switch off any sockets or appliances the water could reach at the consumer unit, but only if the consumer unit itself is dry.

Is the blockage yours or shared? Read the chambers

You can usually tell whose blockage it is in ten minutes. Drains fall towards the sewer, so a full chamber means the blockage is at that chamber or somewhere after it, and an empty chamber means the blockage is before it. Work downstream from the house.

• Find every cover on your side. There is often one near the back door, one at the side of the house and one in the front garden or drive. The one nearest the road is usually the last on your run
• Look into the chamber closest to the house first. Empty with a clean channel at the bottom, while the house is backing up: the blockage is in the pipe between the house and that chamber, and it is yours
• Full, but the next chamber towards the road is empty: the blockage is in the length between the two. If both chambers are inside your boundary and serve only your home, that is still yours
• Every chamber you can see is full, right up to the one nearest the road: the blockage is at that last chamber or beyond it. Check whether the neighbours have a full chamber or slow toilets too
• Sewage coming out of a cover in the pavement or road, or out of a cover that a neighbour’s waste also runs into: report it to the water company. That is almost never a homeowner’s pipe

Flats are the exception. A pipe that takes the waste of several flats in one building normally stays private until it crosses the building’s boundary, so the managing agent or freeholder deals with it, not the water company. Check your lease if you own the flat.

Lifting a manhole cover safely, or leaving it down

A chamber cover is heavy, often rusted into its frame, and sits over an open drop. Lifting one is a normal part of finding a blockage, and a common way to hurt your back or crush a finger. Only lift a cover inside your own boundary, and only if it moves.

• Use two large flat-head screwdrivers, or a pair of cheap lifting keys, one in each slot or end. Lever one edge up a few centimetres, then slide the cover sideways across the frame rather than lifting it clear
• Bend at the knees and keep your fingers out from under the edge. Get help with a cast-iron cover
• A cover that will not move after a few firm levers has probably rusted or been bedded in mortar. Leave it. Hitting it with a hammer cracks old frames and can drop pieces into the drain
• Never lean over, climb into or put your head into a chamber. Drain air can hold hydrogen sulphide and very little oxygen, and a deep chamber can knock you out before you notice the smell
• Put the cover back as soon as you have looked, even loosely. An open chamber is a trip hazard and lets rats and smell out
• Do not lift a cover in the pavement or road. It belongs to the water company or another utility, and it may be over a far deeper sewer

A gully blocked by leaves or fat: what you can clear with gloves

A gully is the small open trap at the foot of a downpipe or under a kitchen or bathroom waste pipe, with a square grid on top. It holds a pool of water to stop drain air coming up. When it overflows onto the patio and the chambers further down are empty, the gully itself is blocked, and that is a job most people can do.

Put on long rubber gloves, lift the grid and take out what you can reach by hand or with an old plastic cup: leaves, silt and moss from the gutters, and grey, soapy lumps of fat from the kitchen. Bag it and put it in the general waste. Keep going until the water in the trap drops and you can see the outlet at the bottom. A gully that has been full of fat for months often has a hard crust around the outlet; break it up with a stick and fish the pieces out rather than pushing them onwards.

Then flush it through with a bucket of hot tap water and some washing-up liquid. Avoid pouring boiling water into a plastic gully, and never use a chemical drain cleaner on standing water outside: it sits there, burns anyone who puts a hand in next, and does little to a fat plug.

If you clear the gully and it fills straight back up, or the chamber next to it is full, the gully is only the symptom. The blockage is in the drain beyond, and scooping will not fix it. If the kitchen sink was what sent you outside, a blocked kitchen sink covers the trap and waste pipe between the sink and the wall.

The gully in the kerb that takes rainwater off the road is not yours. Report it to the council, or to Transport for London on a red route.

Drain rods: when to use them and when not to

A set of flexible drain rods with a plunger and a screw head will clear a simple blockage in a private drain, if you rod from an empty chamber towards the blockage, or from the chamber just before a full one. Always turn the rods clockwise as you push and pull. Turning them the other way unscrews the joints, and a rod left in the drain turns a simple blockage into a dig.

Leave the rods in the shed when any of these is true:

• The blockage is in a shared chamber, a pavement chamber or anything else that serves more than your home. It is not your pipe, and damage to it becomes your problem
• The last chamber has an interceptor trap, a U-bend in its floor with a stopper above it. Rods and stoppers do not mix, and who clears a blocked drain in London explains why that trap blocks so often
• You or a neighbour has already poured a chemical unblocker in. Rods and a plunger splash it straight back up
• The drain blocks every few weeks, the chamber walls are cracked or the ground above the pipe has sunk. That points to a broken or displaced pipe, and pushing rods through it can make the break worse
• The only way to reach the blockage is to lean down into a deep chamber

Sewage in the garden or the house: hygiene and safety

Raw sewage carries bacteria and viruses that cause stomach illness, and it spreads on hands, shoes and paws. Public health advice on flooding says illness outbreaks are rare, provided the clean-up is careful.

• Wear rubber gloves and boots, and cover any cuts with a waterproof plaster before you start
• Keep young children and pets off the affected patio, lawn or floor until it has been cleaned
• Wash your hands with soap and warm water after each session, and before you eat, drink or smoke
• Clean hard floors and paving with household detergent and hot water, then disinfect with diluted bleach. Never mix bleach with any other cleaning or drain product
• Throw away food, including tins, that the water has touched, and bag soaked rugs and cardboard
• Open windows while you clean inside. A strong rotten-egg smell that lingers after the clean-up is worth tracing, and a sewage smell in the house goes through the checks

If the sewage came from a public sewer, the water company can clear the debris from your property as well as the blockage. Ask when you report it.

When it is the water company’s job

On 1 October 2011 most private sewers and lateral drains in England and Wales that connected to a public sewer passed to the water companies. A sewer here means a pipe serving two or more properties. A lateral drain is the stretch of your own drain that runs outside your boundary, usually under the pavement to the main sewer. Both are now the water company’s to clear, free of charge. What stayed yours is the drain that serves only your home and sits inside your boundary, including its gullies and the covers on its chambers.

Government guidance at the time also accepted that, for practical reasons, a water company may take on blockage clearance up to the first chamber just inside your boundary, since nobody can see exactly where the boundary crosses a buried pipe. Whether yours does is a question to ask when you report it.

How to report it, what to tell them and how long they take to come out are all in a Thames Water blocked drain. If it is the water company’s pipe, do not pay anyone else to clear it. If it turns out to be yours, check your buildings insurance or home emergency policy for drainage cover before you book anyone.

When to call someone, and what a drain engineer does

Call someone the same day when the blockage is yours and sewage is coming into the house, when the only toilet cannot be used, or when you have cleared the gully and the chamber is still full. It can wait for a normal-hours booking if a second toilet works, nothing is coming inside and the level in the chamber is not rising. If you are not sure which side of that line you are on, a plumbing emergency or something that can wait sets out the difference.

A drain engineer usually works in order of cost. First comes rodding from the right chamber, which clears most single blockages of wipes, paper and fat. If that fails, or the blockage is hard fat or silt, a jetting machine sends high-pressure water through the pipe to break it up and wash it on. Where the drain keeps blocking, a CCTV survey puts a camera down the pipe to show whether roots, a crack or a sunken joint is the cause, and you should get the footage or a written report. Ask before work starts which they intend to use and what each costs.

If a blocked toilet was the first sign and the chambers outside are empty, the problem is inside the house and a toilet blocked with the water rising is the place to start. When you need someone out, the £60 call-out covers the visit at any hour, 24/7, and the repair price is agreed with you on site before any work starts. Our blocked toilet unblocking page explains how that visit works.