Orginally posted by Charles Watts
...You also have to keep an eye any top opening vents you might have, such as the stand pipes for your water system. *
Just wanted bring this up front and center. Often times we read things but they get lost in the total discussion.
While bringing my trailer out of hibernation, I was going through checking everything. The water in the bathroom had been draining a little slow prior to winterizing, but forgot about it until today. I was thinking about Charles' comment and recalling that when I bought the trailer it had those mud nests all over the place. In, out, and everywhere. At the time, I didn't know about checking the vent pipe.
Today, I pulled off the cap to the vent pipe that services the drains (not the black tank). Sure enough...that pipe was completely closed off with a mud daubers nest.
Next time you're checking, be sure just to pop those caps off and make sure they are clear.