Nasty smell when toilet flushed in another bathroom

[MisterBoy]

Or house has a main bathroom and a couple of ensuite/toilets, all running into a septic tank. The main drain/sink pipe is outside the main bathroom.

Often, having a bath in the main bathroom, there'll suddenly be an unpleasant swamp gas smell. I think I've narrowed it down to when another toilet or shower is running.

It's only this room that you get the smell. I've tried to narrow it down to see if it's coming from the sink/shower/bath/toilet thinking it might be faulty trap, without success.

How can I figure out the cause? Is this a classic sign of a very obvious problem or could it require a lot of investigation?

 

[muggles]

Get yourself a pack of smoke pellets, light a couple and drop them in the manhole. Put the lid on, go inside and look for where the smoke comes out.

https://www.bes.co.uk/hayes-uk-9g-orange-smoke-pellets-pack-of-10-13526/

 

[Mottie]

At a place I once worked at, we used to have some smoke pellets that we took out of a plumbers van. It was fun to set them off under any car that someone was carrying out some electrical repairs/testing on and see how quick they could disconnect the battery.

 

[Hugh Jaleak]

Is the system vented to atmosphere?

 

[MisterBoy]

Get yourself a pack of smoke pellets, light a couple and drop them in the manhole. Put the lid on, go inside and look for where the smoke comes out.

https://www.bes.co.uk/hayes-uk-9g-orange-smoke-pellets-pack-of-10-13526/

Oh that's neat idea

Is the system vented to atmosphere?

yeah the downpipe has a little cowl on top, a couple of feet above gutter height

 

[muggles]

Oh that's neat idea

It works quite well...

 

[MisterBoy]

Not sure the cleaner will be best pleased!

 

[Hugh Jaleak]

yeah the downpipe has a little cowl on top, a couple of feet above gutter height

Can you get a phoro, just want to check its a vent and not an AAV.

Your symptoms would suggest some backing up of waste from the tank into the house drainage system, with associated build up of foul air, which is then struggling to escape when a discharge is made and is looking for the easiest way out.

 

[MisterBoy]

Can you get a phoro, just want to check its a vent and not an AAV.

Your symptoms would suggest some backing up of waste from the tank into the house drainage system, with associated build up of foul air, which is then struggling to escape when a discharge is made and is looking for the easiest way out.

I'll get a real photo tomorrow but it certainly looks like one of these: https://www.screwfix.com/p/floplast-cast-iron-effect-vent-terminal-black-110mm/35136

 

[MisterBoy]

 

[Hugh Jaleak]

Yes, thats vented, so rules one possibility out. Nothing obvious there in the setup that would indicate an obvious issue, system is vented to atmosphere so drainage system and tank should be able to breathe. Only other possibility from the picture, is there a Macerator serving the other bathroom? Looking at the small pipe coming from the right going into the stack, not sure what this is for?

 

[MisterBoy]

@Hugh Jaleak yes well spotted. Two other bathrooms feed in via macerators. One in the loft is never used, the other from our ensuite has a strict 'no solids' rule as the macerator is old and will be very expensive to replace

I suppose could it be possible since the stench pipe vents at eaves height outside this room, the smell could be getting back into the room AFTER venting? Might have to try those smoke capsules...

 

[just pumps]

Turn the macerators off then add hot water and disinfectant, leave for two hours then turn power on. May have to do this a few times to cure smells.

 

[Hugh Jaleak]

Wondering if the pumped discharge is shooting across the stack, and fouling the opposing connection, thereby stirring things up in there, and causing your smell.... Would also be interested to see if you have a shallow trap on the bath, which could also be adding to the issue.

Whereabouts is the Loft WC in relation to the stack, out of curiosity.....

 

[MisterBoy]

I think we have a shallow trap on either shower or bath but I've literally stuck my nose in the plug holes and can't detect they are the source.
The loft loo is halfway down the house

I've got a few things to look at then... Disinfect loos, check the manhole (just out of shot in my photo in the yard), maybe try smoke.
I could try and get someone to flush the downstairs loo to see if that has the same effect.
I'll see what I can find, fun times