sewer gas

[jonesboy]

sometimes there is a sewer gas smell in either bathroom when a toilet is flushed. what's up?
jonesboy

 

[brumylad]

sounds like loss of water seal in one of the U-bends.

try search this forum for trap seal

 

[felix]

Listen for gurgling noises from bath and sink plug holes when you flush the toilet. If you hear anything have a sniff. In fact have a sniff anyway because if brumylad is right there will be no gurgling, just gas.

 

[doitall]

Could also be a stuck Air admittance valve.

A little known fact of life is sewer smell indoors could contain explosive gases, especially when no SVP exists.

 

[Newboy]

It might be worth remembering that sewer gas doesn't smell like most people imagine - have a good look around the pan connectors and (if you can get to it) the connections to the stack.
Might also be worth checking that the traps in tha bath and basin are being siphoned when the toilet flushes

 

[jonesboy]

felix- no gurgling noise... all is quite. brumylad- I went to the crawlspace and checked for water leaks (no dampness around the waste pipe,subflooring). a site search revealed to me that airtight piping is necessary, no cracks! seven months earlier I made a patch of pvc pipe and plumbers putty to repair a cracked waste pipe. the patch was mainly to seal the flange up against the inside of the waste pipe. For both toilet gaskets i haved used a plastic diaphram /rubber o ring system instead of a wax gasket. thanks

 

[felix]

Where is the open end of the soil stack? Is there any chance that gas from here could be finding its way into the house. If you don't have an open ended pipe you should have an air admittance valve instead. If this is faulty it could let gas out as well as air in. If the open end or air valve is blocked (or simply missing) I suppose it's possible for gas to bubble back up through the toilet during or just after the flush.

Doitall is right about sewer gases being potentially explosive. They may contain hydrogen, methane and/or hydrogen sulphide amongst other things. Hydrogen sulphide smells of rotten eggs. Correction, rotten eggs smell of hydrogen sulphide and it's poisonous as well as inflammable. You really don't want it in your house.

 

[croydoncorgi]

An air-admittance valve ('Dirgo') is NOT a complete substitute for an open vent! AIUI, there has to be AT LEAST ONE open vent at the 'head-end' of a foulwater drain. Air admittance valves do what the label says - let air IN. You still need somewhere to let the sewer gases OUT.

 

[jonesboy]

thanks- I copy the explosiveness! on occasion it happens, the smell lasts a few minutes. in the fall a large tree was taken out (& stump grinded) near the house drain to street, maybe roots got into the thing! i am not familiar with an air admittance valve...do you mean vented thru the roof?

 

[jonesboy]

also...brumylad, newboy- how do I check the traps in the tub and basin to be siphoning or for loss of water seal? thanks again

 

[Bahco]

Check my post here

 

[felix]

Croydoncorgi is right about air admittance valves not letting air out. If they did then they would also let gas out. That's why I wondered whether you had a faulty one. That thing venting up through the roof is supposed to be an open end but a bird might have built its nest on top.

If your open end is blocked and you don't have an admittance valve (or it's stuck shut), the toilet contents rushing headlong down the soil stack create a partial vacuum in their wake that can suck the water out of traps.

The next bit is a long shot but that tree business made me think. If you have an intercept trap (a fancy word for a large U bend) between your last manhole and the main sewer you should also have a vent for it. Ours is about six feet away half buried under a hedge. The trouble with these things is that not many people know why they are there. The ones who took that tree out probably didn't give it a second thought and might have blocked it off.

Now we have a slug of toilet contents charging headlong towards the intercept trap and there's no vent. The foul air trapped between the moving toilet contents and the static trap contents will try to escape somewhere. You know your plumbing better than we do. Look along its path for a possible escape hole.

 

[croydoncorgi]

Note to other respondents - this is the US. Local codes and fittings on sewer connections may be different......

 

[jonesboy]

thanks for all you guys helping out! the roof vent is clear and a dip stick-plastic straw, flashlight check was done on the trap- all good! felix- my couldersac has a manhole- no vents in the yard. its' been six days with no foul smell. friday, from the crawlspace i had pushed sagging plumbers putty back onto the wastepipe/ toilet flange`repair'. maybe, air was coming thru!

 

[felix]

I'd say that was pretty conclusive. Sewer gas can come all the way up to the back of your toilet. It's only the water lying in the bottom that stops it getting out into the room.