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
carl