Flappy sound from the soil pipe

[DarthMuppet]

Long story, bear with me. New build, moved in exactly a year ago. we have some oddities with the toilets.

1) The site is an active building site and, just before Christmas last year, the contractors cleaned the external drains to ensure they didn't get called out over the holiday. Nice idea, but this resulted in two of my 3 toilets turning into fountains, making a mess of both rooms. i stopped them, and they said 'oh, means you must have a blockage then'. Wasn't sure what to make of that, so I mopped up and forgot about it.

2) Earlier this year, the same two toilets started backing up, and the bowl would take 5 seconds or so to empty. no big deal, but we did notice that this stopped immediately after dynorod cleared a drain up the road.

3) Since then, i have noticed that one of the two toilets, the downstairs one, makes a flapping sound when water flows down the drain. it is NOT the cistern, as it happens when you pour a bucket of water down it too, just as the last of it has passed. My aim is to find out what that noise is and fix it.

Looking ay my drain covers, they appear to be airtight. With 2) above, that makes me think the entire drain system is airtight, right out into the street and beyond. If that's the case, then the statement that made no sense in 1) now makes total sense - sounds like there's a one-way valve of some kind in my internal soil pipe. If that valve was shut, there would have been no fountain, if it can't shut, that might be the cause of the noise.

Can anyone shed any light on my thoughts above? Never come across airtight drains before, and I can't see anything on the interwebs that can shed any light on it either.

TIA

DM

 

[Gasguru]

Sounds like the drain system is poorly vented...I suspect the noise you hear is from an air admittance valve located in a boxed in section or up in the roof space.
Investigate how the drainage is vented...but if the the contractors are cleaning external drains it sounds like there are problems on site.

Google Durgo... you get internal and external types and they should only be used as a last resource where it's impractical to vent the stack to the open air.

 

[DarthMuppet]

Would I have that valve downstairs, bearing in mind that both toilets appear to be on the same drain? I know I have one on the soil pipe upstairs as I saw it when the house was being built. If there were one downstairs it would need to be above the basin, and the sound appears to come from floor level. I am not certain they are on the same stack and I can’t find the pictures I took.

 

[Gasguru]

Anything goes in new build...you'll need to pull apart the boxing in.

 

[DarthMuppet]

err, no, they can do that themselves. They've done 4 pages of repairs, and to be fair, they are actually pretty good at fixing things when they get down to it. shame they couldn't have built it right n the first place.

Thanks.

 

[Ian H]

Have you looked in your manholes?

 

[dilalio]

Have you looked in your manholes?

Might need a mirror!

 

[Hugh Jaleak]

All drains should be airtight, the whole point of the vent stacks is to allow the drains to ventilate at high level and avoid obnoxious odours at lower levels. Building Control may ask for a test on a drain, and will expect it to be airtight between chambers, then once covers are replaced on chambers, they should be pretty much sealed.

The 'Fountains' you have unfortunately suffered are the result of people jetting drains without taking the risk of Blowbacks into account. Setup you have is very common, with AAV's fitted to Ground Floor WC's, however Contractors jetting and blowing your toilets is not so common.

Basically what happens when jetting is the jet fills the pipe with a 'fan' of water, and effectively seals the pipe, creating a 'bow wave' of pressure in front of or behind the jet depending on direction of travel. This plug of air then needs an escape route, if the upstream end of the drain is sealed with an AAV it looks for the easiest escape route, (usually the WC), with catastrophic results....

Correct practice is to assess the run you are intending to jet, check for laterals and lift any upstream covers to allow the pressure to vent safely. It doesn't guarantee you'll never blow another toilet, but should avoid it in the vast majority of cases. Sounds suspiciously like they've made a monumental balls up with the drainage system which is causing the issues you are describing.

I would be checking very carefully if the Water Company are going to adopt these sewers, and when. Should the building company go into liquidation before the infrastructure has been adopted, then you could be faced with a large bill for sorting out any defects prior to any adoption taking place!