Loud explosion while backwashing black tank

wagonmaster2 wrote:
I have been using the flush connection for years to fill the black tank with fresh clean water for a final wash-out after dumping without any problems. But last fall while the tank was filling, and probably had gotten 1/2 full, I went inside, opened the toilet valve to watch the water level and see if it was clean, and the rush of air blew what little water was setting in the stool out into the bathroom. I have no idea what happened this time that didn't happen many many times over the last 10 year of owning this motorhome but believe me I'll not be filling the black tank this way again, especially after reading about OP's experience.

Could this be an indication the roof vent for the black tank might be stopped up or clogged from inside the tank? Doens't seem like there should be any pressure build up in the tank, which might also explain what is happening here. Didn't intend to highjack this thread but thought my experience might add to the query.

Yes that 'air rushing out of toilet means vent line is blocked or clogged.
Blocked......could be vent line dropped down and water level blocked it off.
Clogged......could be from birds nest/mud dabbers etc.

Tanks do not do well with build up of pressure.

OP:
Tank could have ruptured, flush connection blew off of tank, vent/toilet to tank line could have blown out of top of tank

But from the sound of all the water running out of underbelly......ruptured tank would be my guess.
Especially seeing as you have overfilled it on prior occasions and stressed the tank