Fred,
I have yet to enjoy that experience but one could certainly see how that mistake is made.....I think by all rights Beaver should have put a huge caution sign over that water inlet.
There is probably a need for invention here, much like a car airbag arrangement. When the sensor of impending disaster in the vent pipe sees the brown brew heading for the roof, it then anticipates the creation the "Geyser Of Doom". Through the miracle of modern science it then blows open a settling pond bladder on the roof, sounds the "all hands leave the deck " voice alarm that enables at least a minute of escape time for us retirees. We do move slow...
I readily give up my patent rights to someone who has actually had the experience like yourself Fred :-)
Later Ed