Bathroom Ensuite issues

Rafloution · 11-03-2026 10:22PM #1

Hi all, looking for some advice from folks who know a lot more than me (House 6 months old). House with ensuite in main bedroom. We noticed a smell and drain flies coming from the shower when being cleaned etc. Understand the seal is used in the shower when full to block out the smell etc. However we noticed that it wasnt quite right.

Anyway camera down the shower trap, I get to the pipe where toilet and sink joins, I see water sitting probably a few mm. When flushing the toilet I see water go one way and then slowly after a few seconds I see it rushing back the other way.

Seems the pipe is probably slanted/too straight. So arguing that with the builder.

When plumber put water down the vent stack it pushed old waste out too so in their eyes its fixed, so im pretty sure there's a slope albeit the wrong way.

What I would like to know is, should there be 2-3mm in the manifold? How do I push back on plumber and not be fobbed off. Cheers

blackbox · 11-03-2026 10:31PM

The trap in the shower should have water in it that prevents any smells from coming up.

If this is properly in place a possible problem is that the sewer pipe is not properly vented.

Time for changes · 11-03-2026 10:36PM

Or maybe the pipes aren't at the right angle. I don't think water should be going the opposite way but stand to be corrected.

Rafloution · 11-03-2026 10:40PM

https://www.boards.ie/discussion/comment/124305468#Comment_124305468

thanks understood, that part works fine. We're talking about below that, where the connections join between toilet, sink and shower before going to soil stack

blackbox · 11-03-2026 10:52PM

The sewer pipe will always have smelly water.

Under normal circumstances the trap prevents this smell from coming up.

If the sewer is not properly vented, smelly air can be forced past the trap.

10-10-20 · 12-03-2026 10:15AM

https://www.boards.ie/discussion/comment/124305551#Comment_124305551

I agree, but I'll add that in all cases the piping should have sufficient fall on it, and this can be a problem with any type of sanitary ware which isn't on the external wall. Often the fall is minimal due to distances and obstacles, throw a elbow bend in there too and you'll see back-pressure and back-flow. Did the plumber measure the fall when he was there?

But at the end of the day the u-traps should be functioning to prevent all smells and flies, and if it's not then that also needs to be investigated, and it could be the venting that's causing that. If the house was built as part of an estate then checking with neighbours whether they have similar issues might throw up some answers.

Bathroom Ensuite issues

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