If tightening the collar doesn't fix the leak, you might have to disassemble the p-trap and examine/adjust/replace the plastic slip joint washer.
Usually tightening the collar does the trick (hand tighten only). I tighten/check all mine at least once a year.
Scott and Liz - Southern NM
2012 Wildcat Sterling 32RL - w/level up (best option ever)
2007 Chevy 2500HD 4dr short bed Duramax w/allison
Reese Fifth Airborne air ride king pin coupler with Sidewinder