why does my downstairs loo smell of rotten eggs?

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As part of a refurb before moving into our current house, we replaced the loo and sink in the downstairs loo. I believe the builder did that bit himself rather than the plumber. Only the loo itself was changed, no new drains etc done.

The loo reeks quite often, not all the time but enough to be a nuisance. It's particularly bad in the morning after the house has been shut up at night. The builder has been back and faffed about with it a couple of times to no avail - so either he has no idea what's wrong or he does know and it's going to cost a lot. The plumber says it's not the kind of thing he does, that it's probably drains.

The smell is not faecal, it's rotten egg - cabbagey. We have a pipe with a vent sticking up outside the loo. What's likely to be wrong and who do I need to get in to fix it?

The builder is saying we must be putting nappies etc down the loo - we don't even put baby wipes down it.

Do you know how the loo vents?

Is it through an air admittance valve or svp? You could have a blocked vent pipe if you notice the level of water is low sometimes. Or could you get the trap on the sink checked, or the sub floor in case of leaks. If the system is not properly vented, the low pressure can lower the water in the traps which will allow sewer gases to enter the room.

Get a qualified plumber to look at it.

Could it be your light fitting, check to see if the smell us coming from there. That gives off a terrible smell if it is overheating.

It is the drains. You need to get a different dude in. A decent dude wouldn't be passing blame.. He would want customer satisfaction.

That is absolutely the type of thing a plumber does, I would get a new plumber.

maybe check flooring around toilet bowl isn't rotten from men missing (gross but common!)

I had this problem, still got it, just found out its a collapsed drain!

However ours is a shitty smell

It was a big project overall, with a builder in charge who subcontracted to plumbers etc. For some reason, he didn't pass the downstairs loo to the plumber, he did it himself. I'm really not sure why as the plumber installed the new bathrooms in the rest of the house and put in gas central heating and all new water pipes - withholding one loo from his brief seems randomly odd, Hence plumber is not interested as he didn't do that and it's not part of what he's been paid for. Builder has not finished a few bits and so we've not paid him the final amount due yet - he is very unhappy about this but the contract clearly states it's due after completion of the work and he hasn't completed.

He's now trying to blame us for the loo but it was like that before we moved in and he admitted it at the time, though only verbally.

I don't know what the loo vent is called - it is a black plastic pipe sticking up out of the ground on the wall outside the loo and it has slits in its lid/top - I assume that's the vent?

Floor is concrete, so not rotting.

Thank you all for the advice.

google "Durgo"

it is a brand name and there are others.

slits in the top don't sound right. I hope he has not just fitted an outdoor terminal intended to keep birds nests out, with no valve. You could photograph it and ask at a plumbers merchant what it is.

put a polythene bag over it and tape it down overnight, see if the smell stops. The valve is very easy to take off and change for a new one so I'm puzzled your builder and plumber haven't tried it.

You may however have a leaking joint or pipe under the floor, which is much more troublesome.

Some plumbers would rather work with clean pipes and baths than with shitty drains. Who can blame them? Ask around for recommendations of a hardened old drain man.