Now i am no plumber so please excuse any wrong info anyway my mom had a bathroom installed about 3 years ago any way as a shower was added to the existing waste system she suffered a little back wash. anyhow she neglected to tell me about this until today when a little back wash turned into a severe problem i have managed to gain access to the waste pipes and as she has a cast soil pipe that access is impossible the bathroom installer run all the waste pipes together to the single point on the soil stack nightmare. she lives in a flat so even the kitchen waste and washing machine also run into this waste. my question is should i install air admittance valves ,hepvo valves ,bigger pipework i am very stuck and all help would be greatfully appreciated
First I think you ought to make sure that the pipework is clear of debris or partial blockage. There could well be grease, soap scum, hair and all sorts of nasties down there. An indicator of this is that the problem has suddenly got worse.
Secondly you should consider fitting the HEPVO self sealing waste valve in the shower and bath waste - just make sure they are fitted the correct way round!!
An AAV won't help in this scenario as the purpose of this is to prevent syphonage which is why I asked what you meant by backwash.
Ideally the waste from each sink, bath etc should be separately run into the stack to avoid this happening. However from your description this might be a challenge.
Following rosebery's latest post, take apart as much of the drain sysyem from the bath, shower, sink and washing machine as you can. Then clean them all out in the toilet. Before you put it all back together push a hosepipe into the final bit of pipe running to the soil stack and any other bits that you can't remove and flush them through.
Note, however, that I'm no more of a plumber than you are.
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