En-suite shower water seal getting sucked out by toilet

[pcdj]

The new house we've moved into has a couple of tiny en-suites fitted in two of the bedroom - a shower, toilet, and sink - but the showers rarely get used as they're not too spacious.

Whilst the showers don't get any use the toilets do, and whoever fitted them has plumbed the shower drain to the same waste pipe as the toilet. It's become obvious that the water seal created in the shower drain is getting sucked out with every toilet flush - and so the tiny en-suite room gets filled with waste gas, and it stinks.

I've taken to periodically running the shower to ensure the water seal remains in the drain, but I'm hoping for a more permanent solution. The showers don't get much use so plugging up the shower drain in some semi-permanent style would be fine - something akin to a rubber toilet plunger stuck over the shower drain is what I have in mind, but obviously that's a bit of a bodge.

Is anyone aware of anything on the market that would solve this and wouldn't require taking up the floor/shower tray and modifying the piping?

 

[Mottie]

Surely thats because there is no vent/ stack pipe on the toilet waste?

 

[pcdj]

Possible. The piping between the toilet and the shower drain can't be any longer than 60-70cm, so I would've thought it'd still have some suck at that distance - even with a vent pipe in place.

I also don't meant to give the impression of "one flush and the shower seal is broken" - it takes a week or two; maybe slightly longer. The water level in the shower drain doesn't seem to need to drop by much to lose the seal - possibly 5-10mm or so - which can't be more than perhaps 50-100ml of water, so it's like the toilet is constantly "sipping" at the shower drain.

 

[Mottie]

Are you sure it’s not just drying up? Our villa in Spain suffers the same problem when we don’t go out there for a while. Stinks the place out - very first thing we do when we get out there is run the showers, sinks and bath just to fill the traps up. Maybe just run the showers once in a while or as you say, fit a couple of tight fitting plugs.

 

[jj4091]

may be something here that would help, though not sure where you would fit one anti syphon valve

 

[Madrab]

All depends on how the system has been pipped. I'd suggest a closer look to see how it's all tied together.

You would rarely have the shower and toilet on the same pipe unless the shower tray was above the level of the toilet's soil pipe and the shower waste then ran into the top of that soil pipe.

More normally the shower and basin would share a separate waste into the stack.

 

[Gasguru]

Run the shower to ensure the trap is full and then measure the water seal with a wooden stick.
It's very common for incorrect traps to be fitted with an insufficient seal for the pipework length and drainage layout.
Shallow depth traps should only be fitted on short runs to a hopper but when space is tight ignorant installers use them.

 

[Hugh Jaleak]

Something isn't right, the WC shouldn't pull the shower traps if it's been plumbed correctly. Where doe the soil pipe go in an upwards direction? If it's terminated inside the room with an Air Admittance Valve, (AAV), then I'd also look at this, possible if it's stuck shut, that would cause your syphonage issues, if it's stuck open then it's likely the cause of the smell.

 

[pcdj]

Unfortunately I don't think it's been plumbed correctly.

Here is a rudimentary drawing of my loft. The empty black box to the right is my neighbour (semi-detached property). As far as I can make out from looking in the eaves of the loft there's one rather fat (6" diameter?) pipe exiting the en-suite - the red line. There doesn't appear to be a secondary pipe that would carry the shower waste, so I assume it's plumbed into the same pipe. It carries the entire distance of the front of the house, turns a corner and does almost the entire distance of the side of the house until it hits a vertical stack - after that it turns another corner to a downpipe and into the sewer.

Unfortunately I can't get access underneath the en-suite to check if there's an AAV due to the tiled floor.

 

[Hugh Jaleak]

It is normal practice to connect wastes into the soil pipe from the toilet, but it is how these wastes are connected that is crucial. Difficult to say exactly without dimensions, but that looks to be a long horizontal run from the WC to the vertical stack, which could well be the cause of your issues. If stack vents to atmosphere through the roof then an AAV isn't required on that end.

Unfortunately I dont think there is much you can do without accessing the underfloor, but I have to wonder if you may benefit from fitting an AAV adjacent to the WC. The AAV must be above the spillover level of the highest appliance though, (usually the basin), so will need to be boxed in above floor level.