based upon what we are seeing at the dealership, for folks with new campers and/or folks taking their campers out of winter storage, I recommend that one of the things you check is the tightness of the sink (and shower where possible) drain connections ..... best picture I could find in a quick search:
in new units it is best to check all fittings after each towing until you find they have seated (kind of like checking the torque on lug nuts until they all seat) .... on units that have been in winter storage, temperature changes seem to affect the tightness of some fittings while others don't seem to be impacted
Jim