How do I lift a manhole cover and read an inspection chamber?
Lifting a cover safely, what you are looking at inside, and how the pattern of full and empty chambers locates a blockage before anybody puts a rod down anything.
- Difficulty
- intermediate
- Time
- 30 min
- Read
- 5 min
- Safety
- warning
Short answer
Clear the seal, use proper keys or a bar with two people, and lift with your legs and the cover close to your body. Inside, look at the channel, the branches joining it and the water level. Then lift the chambers in order from the house outwards: the last clear one and the first full one bracket the blockage.
Being able to open your own inspection chambers is the difference between guessing about a drainage problem and knowing. It is also how you find out what your drainage layout actually is, which matters whenever anything is built, blocked or disputed. The technique is straightforward; the safety points are the ones worth reading twice.
Safety
What you'll need
- Manhole keys, or a strong bar and a claw hammer
- Heavy waterproof gloves
- Eye protection
- A torch
- A bucket of water (optional)
- Something to cordon the opening
Step by step
- Identify the cover type.Cast iron, usually recessed or with two keyholes and heavy. Modern plastic, light with a simple lift-out lid and often a screw or clip. Recessed block-paved covers, which have a tray filled with paving and are very heavy indeed. Knowing which you have decides whether this is a one-person or a two-person job.
- Clear the seal.Old cast covers are bedded in grease or mortar and set with grit. Run a bolster or an old screwdriver around the whole rebate to break the seal before you try to lift. Trying to lift a sealed cover with a bar is how covers crack and people hurt themselves.
- Use the right lifting tools.A pair of manhole keys that hook into the keyholes and let you lift with two hands from a standing position. Where the keyholes have corroded away, a strong bar through the hole or the claw of a hammer will do, but the keys are inexpensive and much safer.
- Lift with your legs and slide it clear.Squat, keep your back straight, keep the cover close to your body, and slide it to one side rather than carrying it. On a very heavy cover, two people, one on each key. Put it down flat, not on edge.
- Guard the hole immediately.Before you look at anything. Something across it, or a person standing by it, every second it is open. This is the point at which people fall in, and an inspection chamber is deep.
- Read what is inside.The base of the chamber is a half-round channel carrying flow from the inlet to the outlet, with branch channels joining it from the sides. Follow the channel: where it comes from and where it goes tells you the direction of flow and what connects. Note whether there are branches you did not expect.
- Read the water level.A healthy chamber shows a shallow flow in the channel and a dry benching either side. Water standing above the channel means it cannot get away downstream. A chamber full to the top means the blockage is downstream of it.
- Lift the chambers in order.Start nearest the house and work outwards to the boundary. The last chamber running clear and the first one full bracket the blockage between them. If the final chamber before the boundary is full, the problem is downstream and is the water company's.
- Close up properly.Check nothing has fallen in, clear grit from the rebate, and reseat the cover fully so it does not rock. A rocking cover is a trip hazard and it lets silt in. On old cast covers a smear of grease in the rebate makes the next lift far easier.
Tips
- Do this once in dry weather when nothing is wrong, and map your drainage. Doing it for the first time with sewage rising is the wrong time to learn.
- A recessed cover full of block paving can weigh a great deal. Get help, or use a proper lifting device.
- Photograph the inside of each chamber. It is the drainage plan you will wish you had when an extension is being designed.
- Never put your face over an open chamber to look down. Use a torch and stand back.
If it doesn't work
Cover will not budge
Cause: Sealed with mortar, grease and grit, or the paving has been laid up hard against it — Fix: Cut around the whole rebate with a bolster before lifting. Do not use more force on a sealed cover — that is how they crack.
Keyholes have corroded away
Cause: Age — Fix: A bar through the remains, or two claw hammers hooked into the edge. Then plan to replace the cover: a cover that cannot be lifted is a cover nobody will lift in an emergency.
Chamber full of water and debris
Cause: Blockage downstream — Fix: Do not start rodding from a full chamber. Work outwards to find the first empty one and rod back towards the blockage from there.
Chamber full of silt but flowing
Cause: Years of accumulation, common where a chamber has an unused branch — Fix: Scoop it out with a trowel and a bucket. A silted chamber is where the next blockage will start.
Roots growing through the chamber
Cause: A tree root has found the joints and entered the drain — Fix: Cut back what you can and get a CCTV drain survey. Root intrusion usually means a damaged joint and it recurs until the pipe is repaired or lined.
Cover rocks after refitting
Cause: Grit in the rebate, or a distorted frame — Fix: Clean the rebate thoroughly. If it still rocks, the frame has moved and needs re-bedding.
Questions people ask
Am I allowed to open a chamber on my property?
Yes. Chambers on your land, on your private drainage, are yours to inspect. A chamber in the highway or one clearly marked as the water company's is not, and should be left to them.
What if it is a shared chamber?
Common in terraces, where several houses join into one run. You can still inspect it, but a blockage in a shared drain may be a shared responsibility, and beyond the boundary it becomes the water company's lateral drain.
Is the smell dangerous?
Sewer gas at the surface of an open chamber in the open air is unpleasant rather than dangerous. Inside a chamber it is a different matter entirely, which is why entering one is never a householder job.