We have a downstairs wet room

The toilet isn’t connected to an outside stack as we couldn’t get it through planning when the extension was done.

The foul pipe is connected to an AAV (air admittance valve) in the understairs cupboard, which is next to and ‘up stream’

We keep getting ‘foul’ smells in the wet room as flushing the toilet pulls the water from the shower trap rather than the inlet valve. I’ve renewed the inlet valve and it solves it for a few months but it always starts again.

I have a pile of 4-5 inlet valves now and at £20 a go I need a better solution.

???? Any ideas?

Anti syphon trap in the shower?

You need anti-vac traps by the sound of it.

Yeah but shower trap and run set in screed and tiled over with hugely expensive Limestone tiles 😯

….. hmmmm

Offending shower trap

Right, just checking it was screeded in and it is, but the 40mm waste for the shower exits into the understairs and then connects so I could cut the 40mm pipe and add a HepVo before it joins the soil pipe.

Reckon this would work?

I think it pulls the shower as it’s a shallow trap

Bump for the plumbers as the finish @ 3

HepVo >?

I’m not a plumber but I’ve used 40mm hepvo traps in line to solve a similar problem and it worked superbly.

Does the soil pipe only serve a single storey? Is there a vent elsewhere on the system? If so you could probably get away with a stub stack, no need to vent it.

Yes, soil pipe is for downstairs extension only no other vent on the system other than manholes on the run and the AAV.

(this sounds wrong and it is but it’s an old house and had a cast pipe that sat under the house that cracked so was decommissioned and the main stack connected to next doors drain)

So no other soil pipes connected into those manholes. it doesn’t have to be on the same run, the head of the drain run should be the one that is vented.

Yep, no other soils, the AAV is is at the top.

Based on your description, an air admittance valve on the shower waste pipe work is your simplest and best solution. This is a design error on your plumbers part and quite common amidst other faults unfortunately. It’s not a simple mistake, it’s a glaring oversight and partly why plumbers in general are so unilaterally mistrusted and disliked. It really p—es me off.

.

Can’t blame the plumber on this one as he warned it was wrong and tried to make the best of old house/bad architect plan/ no ability to connect to or install an outside stack.

While caveating it wasn’t right

The rest of his work was excellent (rest of house)

I somewhat disagree. As a plumber and having been in situations where I have been asked to do something I knew could be problematic, I advised my customer and in every case, once informed, they agreed to adjust their plan to accommodate my recommendations. Besides, I would have planned your job based on the existing soil pipe arrangement and included anti syphon traps or modification to the set up to prevent this problem.
Better to resolve the issue before it’s even brought up.
I DO think it’s your plumbers problem.

Well put a Macalpine 1 way trap in, we’ll see if it fixes it

Yep, Fixed it! Yay 😀

(everybody who was worrying about the outcome can now sleep again)