Nasty niff in bathroom

[Jackie]

Having removed some tiles and peered under the bath I find that a very shallow trap has been fitted with no room to fit a deeper one.

 Every couple of days in the Summer the water level in the trap falls enough to allow fosse gasses to escape into the bathroom. There are no visible leaks and no suck-down effect that I can detect, there is a roof mounted vent.

On digging a few holes outside I find that the bath, sinks and all other waste water sources, but not the toilets which use a separate 100mm pipe, are connected to a 40mm waste pipe which runs to the fosse. The bath is at the end of the line furthest from the fosse. I had thought to fit, using four 45 degree bends and a straight piece of 40mm pipe, a trap outside where the pipe exits the property and as close to the bathroom as possible. The idea being that this short section would be lower than the rest of the pipe and should stay filled with water blocking the gasses from rising up to the bath plughole.

Do you think that this would work or is some sort of hydraulic action going to suck this out when water passes through it or when water is passed into the pipe from other sources further down and closer to the fosse? Would be grateful for any opinion ..................John in 79 

[Michael]

John leave the bath waste alone , remove the trap on your basin and fit a anti/syphon bottle trap instead that should solve the problem.

[Jackie]

Thanks Michael. There are bottle traps fitted to the two sinks in the bathroom already, I don't know if they are anti-syphon or not. Cannot fit one to the bath, which is the source of the nasty niff, as there is just not room in terms of depth. There is no evidence of other waste water output sucking out the bath trap at all, it is just so shallow. So what do you think of the idea I have put forward, non-starter or what?....................John in 79

 

[Michael]

John. Still say fit anti/sypon trap to basin or remove shallow seal bath trap and install deep seal s trap[chisel hole to fit].Or leave trap in postion and fit an inline running straight anti sypon to pipe .Other way is to fit somewhere on your 40 or 50m waste pipe a anti/vac valve {must be fitted above the level of your wc cistern water level].you can bye them in sizes from 28mm up to 100mm

[Michael]

anti/vac valves name in english is called,dirgo valve.Stops soil and waste pipes syponing[not sypon or bye,]it was bit late and one tot to many.happy plumbing.

[Jackie]

Further to my original posting I have installed the home made trap outside below ground where the bath and sink waste water pipe exits the property and it seems to work....no more nasty niffs.

I have found one thing that seems a bit strange and that is all the waste water from everything except the toilets runs into this 40mm pipe. The loos have a 100mm pipe running alongside. The two pipes are only connected together just as they enter the fosse. This is strange as you would think it would be better to put all waste water into the main soil pipe to help it keep flushed out. Maybe the owner intended to put in a grease trap on the small pipe or anticipated that there would eventually be a requirement to do so.

There still seems to be some disagreement on this and other sites as to whether a grease trap is required or not on fosse toutes eaux. Certainly the guy that emptied ours and the fosse inspector said it was not. Could the rules depend on when the fosse was installed I wonder?.....................................John in 79

[Michael]

[quote]Having removed some tiles and peered under the bath I find that a very shallow trap has been fitted with no room to fit a deeper one. Every couple of days in the Summer the water level in the trap f...[/quote]

I think you are right, the previous owner might have thinking  about fitting a grease trap.And you certainly would have had a bit of draw on the 40mm waste.It sounds like your open vent on the stack pipe is wrongly postioned[if you have one].It would allso be wise to fit the grease trap john.Any problems can be solved with anti/syphon traps and dirgo valves.happy plumbing.