Manhole disaster

27 Aug 2022
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United Kingdom
I moved into this property around 18 months ago. 1930s semi with a small kitchen extension to the rear which backs on to the garage to the front. There is a door between garage and kitchen, with the garage level two steps down.

Recently I noticed a bad smell so checked out the manhole cover out on the patio and surely enough it was backed up. I tried to hose and drain rod which to my huge surprise resulted in drain water leaking out into the garage.

Further investigation has revealed there is another manhole cover under the kitchen extension the corner of which is just barely visible via the stairs the drop down into the garage. It was here that water was overflowing. The stairs seem to drop to the ground level, level to the top of the cover. But there doesn’t appear to be a proper cover in place.

Turns out that whoever built the extension or the garage access has half exposed the old manhole and not sealed it up correctly. I’m at a loss as to what to do here.

It would seem I now need to rip up the entire kitchen floor to have full top down access to the manhole to replace the whole manhole with something fit for purpose.

Either that or is it possible to somehow fill in the manhole altogether? It has two inlets, one from the soil stack, one from the garden manhole and one outlet which runs into the street so could you add a top to the drain and fill it in?
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Crude plan below will have to get pictures of the chamber. I can only see the very edge of the chamber lip at the moment as the timberwork for the stairs is preventing opening up the side where the chamber is located. Going to take that apart to get a view tomorrow.

Worth mentioning as well, I couldn't find a chamber at the front of the house, drive is gravel so may well be under the gravel, or there isn't one?

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You show a drain line leading into the patio manhole where is that line coming from?
Where is your soil stack?
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You cannot just fill a chamber in, it would have to be dug out and the pipework replaced, but that doesn't address the issue of why the chamber was put there in the first place. The soil stack is shown coming in on a branch, this run needs to be accessible, currently that appears to be from the chamber. I would suggest you best and easiest option, would be to replace the chamber cover with a suitable internal, screwed down, sealed type, which can be lifted in dire emergencies, but, if fitted correctly, will seal liquids and gases in.

Also, unless another chamber is located in the driveway, (and given the age of the property, there is a fair chance there will be another chamber with an 'Interceptor' on the outgoing pipework), which could also well be the problem in the first place. Interceptors are prone to blocking, waste then either backs right up into the house drainage system, or sometimes, it escapes through the rodding eye, before slowly backing up into the incoming pipework, and eventually blocking that up.

I'd be looking for another chamber out the front before doing much more.

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