Sewage smell bathroom

[Alexkx3]

Hi all,

Common problem but wonder if any old hands can help me pinpoint the cause. There's a sewage smell in a client's ground floor bathroom, which they say seems to occur when the bathroom is used. (They've gone away on holiday and come back and it smells fine).

There is no external vent, the system is connected to an internal durgo valve which is over a meter above the floor in room adjacent to the bathroom. I've flushed the toilet and the traps don't seem to be emptying. I've attached a diagram of the set up, the toilet is going straight into the main soil pipe which connects to the main sewer, and the sink and bathtub first run into a stub stack which then connects to the main soil pipe via swept T.

I'm thinking it can either be one of several things:

Back pressure in sewer causing gas to come up through the traps.
Durgo valve faulty and causing traps to drain enough to let gas in.
Loose soil pipe connection to toilet.
Shallow p-trap on the bathtub not selling in sewer gas. (It gurgles a lot when the sink tap is running).

Any thoughts would be much appreciated!

Thanks,

Alex

 

[Hugh Jaleak]

Id be looking for a blockage downstream first. If the drain is blocked, then any discharge of water needs to displace the equivalent volume of air, so this foul air is looking for another way out. Would explain why no smell when this room is not used.

Would also investigate gurgling on bath trap. Shallow traps aren't suitable for baths connected to a stack or drain, look at either putting a deeper seal trap or swap for a Hep V o type valve.

 

[Elkato531]

Shallow bath traps should only be fitted where the bath drains direct to a gulley and not into a stack. It would be top of my suspect list. Ask them to run a bath tap briefly after other appliances have been used and see if that stops the smell. If it does, change the bath trap.

Also check the durgo. They do stick. If it isn't opening properly, the water could be getting pulled from the bath trap in order to equalise pressure.

 

[Alexkx3]

Thanks for the reply guys. I'll give the hepvo trap a try and also replace the durgo. I'll also run some drain unblocker as well.
Hopefully I wont need to install an external vent, but I know internal aav systems dont deal with positive pressure well.

 

[Hugh Jaleak]

Chemicals are pretty much useless on drain blockages. Only proper way to clear them is rods or jetting. If you have used any chemical, be extremely careful, and warn anyone lese who may need to work on the drains!

 

[Ian H]

If you don't find a blockage try a smoke bomb in the external manhole. Look and sniff for any signs of it inside.