Non-return valve for shower outlet

Is your u/p trap defective or the water seal dried out?

I'm guessing that shower doesn't get used much and the trap has dried out. Just run it occasionally to make sure the trap is full.

There are three that work on the same principle:

Toolstation has Macvalve and Viva Magna:

Many thanks. My problem with that type of fitting is lack of access - which is why I wondered about the Australian non-return valve.

To answer other points made - I don't think the trap is defective, it's not very old, but it definitely isn't used much. But it has always been slightly smelly - and my wife has a very delicate nose!

Keith

Recent high winds may have emptied water traps with the venturi effect sucking air from the stack vent. Not noticed with toilets/wash basins in regular use.

Good point, but this issue has been present for a long time. Originally there was no stack pipe for this outlet, and we did, in fact, have one fitted. This helped a bit, and the smell does vary, so perhaps the wind is a factor here. Is the a special kind of cowling for the top of the stack pipe which would prevent wind blowing down it.

Keith

a little bleach and caustic might be what's wanted. Caustic can eat up the debris causing the whiff.

NT

But we have a septic tank - so no bleach or caustic!

Do you keep the trap clean? I know the trap on my shower needs regular cleaning, like once a month, to clear out the hair and jelly-like deposits that seem to accumulate in it. If your shower isn't used much, I imagine that muck could start to smell. And are you sure it's not something else causing the smell, the hand basin or toilet for example, assuming you have either or both in the cloakroom. Does the cloakroom have a concrete or suspended wood floor, and if the latter, could there be a leak in the under-floor pipework allowing smells to come up through the floor?

We had a septic tank. A little bleach in moderation is OK. You only need a little to kill the bugs in a trap.

there are other things you can use to eat stray matter. Hot water & detergent, acid, steam cleaning etc

NT

The traps for showers tend to smell after a while as they become clogged with hair. Usually the trap can be removed by lifting the cover and twisting it out, then clean it.

There are three that work on the same principle:

Toolstation has Macvalve and Viva Magna:

The worst thing for a shower is to use solid bar soap rather than shower gels and liguid soaps. Solid soap causes hair and stuff to coagulate into a scum.

Best advice anyone ever gave me was to ditch tablet soaps from the home.