I have an ongoing issue with a pvc trap in a rental unit. I have had a plumber repair it at least 6 times in 3 years, it is a pvc trap that is under a kitchen sink with a disposer and dishwasher connected to it. The pipe in the wall is cast iron and the stub out is pvc with the trap. I have had the trap crack at least 4 times and loosen up and leak at least a dozen times, my plumber thinks the tenants are dropping pans in the stainless steel sink and cracking the trap, i was thinking of making the connection to the wall stub less ridgid by cutting the pvc and adding one of those rubber fernco couplers, this way the trap can flex without breaking. My only other option is to use one of those cheapo flexable traps and hope it lasts, this is getting to be an expensive problem, have replaced the cabinet twice and paid my plumber to replace the parts way too many times, plus I am getting too old to keep going over there and tightening the trap every other month, anybody have any other suggestions? Thanks!