Speaking of fw tanks...I was filling with water before setting up camp and couldn't get the water to go in as usual...it burped and splashed back like never before. You could feel air being forced out the inlet past the hose. Hmmm. Crawled under the coach and found the overflow tube, sure enough a mud dauber wasp had plugged it. An ignition key for the truck (old school) was the right size to dig the mud out. Filled fine after that. I guess that's another thing to check when readying the coach for travel.
As water goes in air is forced out the overflow tube, unless it's plugged.