My funniest bonehead was when I decided to clean my black tank. I dropped a bunch of laundry detergent in the tank and used a sprayer wand to agitate it. Then I proceeded to fill the tank. I was standing right under the vent pipe and a guy walked up and we started talking. I forgot all about the water pouring in to the toilet! Next thing I know brownish soap suds start dropping on my head! The other guy's jaw dropped! I looked up and soap suds are pouring out the vent stack.
I ran inside and stopped the water just at the edge of the rim of the bowl! Did not help that I had a head full of brownish soap suds and the other guy could not stop laughing.