Black tank flush overfill

dougrainer wrote:

Cummins12V98 wrote:

dougrainer wrote:
OK, one thing that can happen when you do this, it can BREAK the 3 inch down tube from the black tank. The Pressure involved when you do this is tremendous. 45 psi or more has filled the black tank and now the tank has expanded(swollen) and popped either the 3 inch down tube loose or the 1.5 inch vent tube loose. We know this because instead of water coming out the roof vent and overflowing on the roof it came out the bottom from the top of the tank. Because the tank broke open at the tank which is a good thing instead of out the roof vent. NOW, if you do NOT fix the problem on top the tank, you will have black tank odor migrating into the lower bottom cavity because it is NOT sealed now. The RVIA standard for both Gray and Black is to hold water when overfilled. With Black we fill until the water is just below the toilet ball valve and on Gray with water coming into the shower or tub. Also, unless you access and clean out the top of the tank and the underbelly and insulation, you will now have a musty smell all the time. Both inside and out. Doug

How do you know this? There is a roof vent there for a reason, I don't see how pressure can be added when there is a vent.

I suggest you start a Black flush and let it go with valves closed. If the pipes to the tank are glued, you will have sewage water coming out the roof top vent. I HAVE NEVER DONE IT! I have FIXED quite a few that customers have done it. AND, if the 1.5 inch pipe is NOT sealed where it comes thru the outer roof deck, you will get water into the roof cavity. With water coming out from the interior ceiling panels and such. Doug