Posting a message to the forum will remove the above advertisement
  1. Checkout our Plumbers Insurance area - heavily discounted Public Liability Insurance and Van Insurance specifically designed for plumbers.

Discuss Sewage smell downstairs toilet in the Plumbing Forum area at

  1. MandyBT

    MandyBT New Member

    I would be really grateful for advice here. I had an extension built and as such the length of sewage pipe from downstairs loo near front door to manhole at back extended by 3m. I'm not sure if builder connected this to the run of pipes joining the soil stack with a y shaped thing but this connection must be past the stack now as the stack got moved round to the side of the house. When the stack was at the back of house it may well have run straight to it. I know where the pipe runs from toilet and the stack is 'round the corner' from it if that makes sense. Would this situation cause foul smells intermittently? Seems worse after rain and I just realised run off from gutters on extension runs into foul near kitchen grid. But its not only when it rains that its smelly. Drains were surveyed nothing detected in way of leaks. Drain man said he thinks fall is 'adequate' . Smell from toilet not sink. My husband has checked the seal. I have a compact flushing toilet maybe not enough water flow for 10m? distance to main drain? I dont think it was as bad 1) when we had larger cistern and 2) when our ensuite above down stairs loo was in constant use (shower & toilet broken due to age and cant afford replacement yet) Would this be solved by getting some sort of stack/valve for downstairs loo? Are you allowed 2 stacks - can't find info on whether a second affects air pressure? Or will the increased through flow of water when we use ensuite again stop stagnation and smells? Smells come into en suite when trap dries out but resolves when I fill up. Hope this all makes sense. I had a plumber round but not a whiff that day as per the law of sod! Thanks in anticipation!!
  2. rasmo

    rasmo New Member

    Sounds like Air seal on WC pan trap or Air seal on basin waste trap if no leaks on pipework. Could be due to excessive air pull on main drain .
  3. Chuck

    Chuck Active Member

    It could be that the sheer volume of water from the gutters is provoking/causing the problem. Are you in a part of the country where 'combined' systems are permitted? If not you should get the rainwater disposed of in accordance with local requirements, typically via a soakaway or rainwater drain.

    It should take a long time (months IME) for a trap to 'dry out' unless the pressure in the drain is fluctuating wildly in which case it can be days. This might be another clue.
    Last edited: Oct 18, 2017
  4. MandyBT

    MandyBT New Member

    Thank you. The guy who did camera removed toilet but pointed out he had sealed it well. What causes excessive air pull on main drain?
  5. MandyBT

    MandyBT New Member

    Thanks. I believe it must be allowed inspector came round a few times and he is meticulous. I would be happy to get rain water diverted the man hole for it is very close not much work there. But, yesterday out of the blue the foulest smell ever appeared weather is dry now for 3 days or so. Hot water and bleach resolved. It's frustrating. What do you think about an extra mini stack/valve would it be a good idea? I'll go mad if I go to expense of diverting rain water and it doesn't work. Thanks again.
  6. Chuck

    Chuck Active Member

    Based on your extra information, you've probably got a 'combined system' and I think it is unlikely that the rainwater arrangements are to blame.

    Just to be clear, are you saying that the smell seems to be coming from around the loo itself and the loo is new?

    If so, there is a rather rare manufacturing defect that happens when the toilet-pan manufacturer doesn't seal a casting hole. This hole connects the rim that channels the water for flushing with the sewer side of of the trap. This allows positive pressure in the drain to drive sewer gas into the bathroom.

    Careful pressure testing should reveal this.