Smell and pressure coming through shower trap

[Kaps86]

Hi all,

Newbie here. Looking for some advise and help please

Back story…..

Some years ago my dad had an extension to his house which included a newly built downstairs shower room. Recently he had this downstairs shower room re-fitted/decorated. Quite a simple set up consisting of a sink, toilet and shower. However after my plumber/fitter completed the job we started to notice a real foul sewage smell coming from the shower trap. I’ve noticed in addition to the smell there was a fairly decent pressure of smelly air/gas coming out of the trap. After multiple attempts and messing with the trap and basket (that holds the water) I think I have stopped the smell/gas from coming into the room. Obviously if I take the sliver lid of the trap off for cleaning etc I notice the smell/gas again as it’s still coming into the trap pipes.



So my questions are as follows…..

1. Is this pressure of smelly air normal to come up through the waste pipe? I assume it’s coming from the soil pipe that the toilet is also connected to. But guessing there shouldn’t be any foul smelling pressure coming back up in the wage pipes?
2. Am I correct in thinking that the small amount of water in the trap/basket should stop smelly gas coming into the room? I’ve checked and with all the trap components fitted, the only way for the gas to come through is through the water, but I’m assuming the water will completely block out the gas?
3. The water in the waste trap basket is only around 38mm deep. I read somewhere that a shower trap water should be around 70mm deep as shallow water won’t block the gas……is this true? Or is the water depth irrelevant as long as the only way in or out of the trap is via the water?
4. My assumption is that there should not be a back pressure of smelly foul gas coming back through the waste pipe, as I’ve read all soil pipes (which the shower waste pipe flows into) must be connected to a vent pipe to rid of gasses? Is this correct?
5. My biggest worry is that I or my plumber don’t know how the builders who created the shower room extension originally layed out the soil pipes and where they eventually lead to? A vent or straight to the sewage drain/pipe outside? The new shower room extension is at the front of the house, but the original vent pipe which sits outside and connects the kitchen and upstairs bathroom is at the back of the house. Therefore the soil pipe which my builder connected to the toilet waste and shower waste pipes we don’t know if it is connected to a vent pipe or simply just connected directly to the waste drain/pipe outside? Is this even allows as I assumed all soil pipes should be connected to a vent pipe? Is there any way of telling?

Extra information

I’ve flushed the toilet in the shower room, run the taps and also run the taps in kitchen and flushed toilet upstairs and none of these seem to pull water from the shower trap. There is still the correct level of water sitting in the shower trap. Neither is there any gurgling or feeling of suction from the shower.

Pictures attached if they help

Would honestly appreciate any advise to my questions as it would give me a better idea of what I’m dealing with



Thanks

 

[Hugh Jaleak]

Ground floor bathroom, appliances are likely to be connected directly to the drain, or possibly via a 'Stub Stack', is there anything boxed in a corner, adjacent to the WC? Given direct connections, a 75mm Depth of seal for basin and 50mm for shower would be required under the regs, but if foul air is coming back into the room, either the trap is getting siphoned out or there is some positive pressure looking for a way back out.

Does everything drain away, and toilet flush ok? Initial thoughts are of a full or partial blockage, which causes the discharge to have to displace the equivalent volume of air trapped in the pipework, which then looks for the easiest route out, i.e. the shower waste. If you flush the WC is there any gurgling or water splashing back out from the shower waste?

 

[Kaps86]

thanks huge for reaching out…..

Sorry if my terminology is incorrect. Still trying to learn the names and how a pipe system is layed out etc. In my post when i say the shower waste pipe is connected to the soil pipe ( I actually mean it is connected to the same pipe that the toilet waste pipe is connected to). The toilet waste pipe is connected directly into a hard brown colour looking pipe which comes out of the ground in the bathroom.

(See attached pic which might make more sense)

Therefore I assume like you say this hard brown pipe must go directly to sewage pipe/drainage outside? Or would this connect to a vented soil pipe at the back of the house? My best guess is it’s not even connected to a soil vent pipe?

No there doesn’t seem to be anything boxed next to the toilet

Sorry I don’t mean to come across sounding silly but could you just break down something you mention in your reply so I understand better as I’m a newbie…..

1. When you say “a 75mm Depth of seal for basin and 50mm for shower” does that mean the shower trap should hold 50mm of water whereas mine currently holds only 38mm?

Yes everything drains and flushes away fine. The toilet flushes and drains fine and the shower drains fine. Even when I flush the toilet the water in the shower traps remains the same and there is no gurgling and splashing from the shower trap. So I didn’t think there would be a blockage and as the water in the shower trap remains I didn’t think there is a siphon effect?

On a side note I also noticed a very slight sewage smell comming from where the toilet waste pipe connects to the hard brown pipe which comes out of the floor. Seems as though the Plummer used a circular rubber seal to seal the connection and when I spoke to him he said he’ll use a silicon sealant to make an air tight seal between the two pipes. My only question is, should there even be a positive pressure at that point in the pipe? Or is this normal and the smell/pressure is kept at bay by the water sitting in the toilet basin?

I just don’t understand what could be causing this back pressure of foul smell gasses? Nor can my plumber sus it out?

 

[HERTS P&D]

Have you checked the manhole/s for a blockage?

Andy

 

[Kaps86]

not checked man hole cover yet, but I will do so. Im guessing here but if there was a blockage wouldn’t that mean there would be issues with the draining of the water from the shower or toilet? Currently the waste water all drains fine.

My biggest concern is that, the positive pressure of smelly gas, will over time build up in the pipe and cause the water which is sitting in the shower and toilet waste traps to start to smell? Is this a correct assumption?

 

[Mister Banks]

The drain doesn’t have to be blocked to cause a buildup of waste, it’s definitely worth checking that the drains are clear. I have to lift a manhole cover and hose down a drain twice a year to clear waste that gets lodged in blanked off pipework.