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