WC backed up

Hi I have a toilet that is backing up and when flushed causes water to bubble out of the shower unit. I have checked all the waste pipes for blockages and am pretty sure that there are non (using an auger, caustic soda and the vacuum plunger things). I have also found the main exit of the waste (from both the WC and sink/shower etc. I have attempted to clean this out by using a flexible auger (5m length) and also poured in some suplhuric acid. The system looks clean but it still backs up. However I noticed whilst unblocking the main waste that whilst the cover was off it didnt back up and everything flowed find. Screw the lid back on and it backs up. Clearly this seems to indicate a blockage further along the pipe? I live in a small block of flats and have the lowest flat, any ideas on how to solve this? I have read about making sure that the vent is clear but I'm not sure where this is? On the roof? By the way the shower is the lowest point of exit for the water and when the builders installed it they didnt do a great job of ensuring a sufficient slope for the waste pipe, but that's a seperate issue. If it is further down the line is it my responsibility or the entire block? Any help gratefully received?

Adrian

Reply to
Adrian
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I suspect that the water bubbling out of the shower unit is the water in the shower trap, pushed up by air pressure in the pipe.

When the toilet waste hurtles down the pipe it increases air pressure before it, and this causes your shower trap to bubble.

When the manhole cover is off, the air pressure can escape that way; with the cover on the pressure rises to the point the shower trap bubbles.

You might be able to resolve it by putting a vent pipe from the shower up to above the toilet waste.

|| Toilet || | Shower ||----------| | || |-----------------|| || || Main waste stack

### || Toilet # ####| | Shower # ||----------| | # || |--------------#----|| || || Main waste stack

vent pipe shown ###

Unfortunately an air admittance valve will not sort the problem, as they are designed for suction pulling water out of traps, not air pressure pushing it out.

Owain

Reply to
Owain

could it be a blockage in the stack pipe, which is presumably another flat's output? If so, theyll clear it themselves.

NT

Reply to
bigcat

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