I had a previous RV with the same problem. Due to improper pipe alignment there was stress on the p-trap joint and the vibration during travel days would cause it to loosen/break and leak.
I had enough straight pipe on the exit side of the trap that I could cut and install a very short section of rubber pipe (like radiator hose) with hose clamps. This removed the tension on the joint and I had no more problems.
You can check for stress by disconnecting the p-trap at the collar and seeing if the two sides don't line up or separate.
Hope your problem is as easily fixed. Good luck!
Scott and Liz - Southern NM
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