Loud explosion while backwashing black tank

[fun2rv]

Today I was doing my regular duty of emptying/backwashing the black water tank. I had emptied both the grey and black tanks and was in the process of backwashing the black tank. Now I know it says not to run the tank sprayer with the black tank shut, but I have always done this and watched the level of the water and shut it off to empty. Of course there has been the couple of occasions that I forgot the time and of course the water has always just gone up thru the toilet and made a mess inside. Thankfully it has always been after I have emptied and rinsed the tank out. But today, the tank wasn't quite full yet and all at once there was a loud boom (like explosion) and water started pouring out of the underbelly of the trailer (2002 3280 Montana 5th wheel). No water came out thru the toilet at all. It was getting late, so I wasn't able to take the underbelly covering off to inspect any of the tanks - will try to do that first of the week. I went on and made sure all the water quit running and made sure the water supply was off and left it alone. Does anyone have any ideas what happened and where or what I should start looking for first? Appreciate any and all help.

[PastorCharlie]

It appears that someone failed to open the black tank drain before flushing to cause manufacturer to post the instructions to open the value first.

There is always a reason for the instructions.

[Ron3rd]

RV-1/2n-FUN wrote:

wagonmaster2 wrote:
I understand you should always open the fresh water fill inlet on the side of the RV if filling the tank from the city water hook-up. This is supposed to keep from pressurizing the water tank and doing damage.

Pretty sure there should be NO CONNECTION between black tank and any fresh water fill!!!!! We're talking bio-hazard here.

Correct, and all fresh water tanks have a vent in them.

[RV-1_2n-FUN]

wagonmaster2 wrote:
I understand you should always open the fresh water fill inlet on the side of the RV if filling the tank from the city water hook-up. This is supposed to keep from pressurizing the water tank and doing damage.

Pretty sure there should be NO CONNECTION between black tank and any fresh water fill!!!!! We're talking bio-hazard here.

[LarryJM]

wagonmaster2 wrote:
I understand you should always open the fresh water fill inlet on the side of the RV if filling the tank from the city water hook-up. This is supposed to keep from pressurizing the water tank and doing damage.

Maybe I'm missing something, but I see no way this would help prevent pressurizing the black tank regardless of the method/source you are using to fill/flush it. They only way is for the vent not to be venting by being lower than the water level in the black tank or being blocked by an obstruction.

Regardless, the point about not overdoing or obsessing over getting it that clean is an excellent point IMO.

Larry

[wagonmaster2]

I understand you should always open the fresh water fill inlet on the side of the RV if filling the tank from the city water hook-up. This is supposed to keep from pressurizing the water tank and doing damage.

[Fordlover]

Lantley wrote:
Lesson to learn from all this is black tank does not need to be spotless.
Don't obsess over the cleanliness of the tank. It's ok to rinse it out but no matter what you do there will always be residual stuff.
Trying to get it spotless can create serious issues. Why get it spotless when all you are going to do is fill it up again?
I slowly learned myself, that obsessing over the black tank is counterproductive. A quick rinse or 2 and be done with it.
While I understand overfilling was an accident, there is no need to fill tank to the point of causing an issue. You should have quit filling long before the point of rupture. Quick rinses is all you need.
If you have odors use chemicals occasionally or as needed to eliminate odors.
Repeated long fills are unnecessary, Especially fills long enough to rupture tank.
Lastly you cannot trust tank monitors to determine fill level. Use a timer. Decide how long it takes to fill tank based on time. I never let my 40 gallon tank go longer than 5 minutes. Using a clear elbow I watch what comes out. Usually one or 2 rinses is all it takes. I also back wash black tank with gray water which works very well.
If it is not convenient I do not flush at all. If I am camping again in the near future I do not flush at all.
Once you get things back in order, I suggest you change to a less rigorous flush routine.
There is simply no need to take the risk of causing damage, think quick rinses vs. long fill ups.

Probably very good advice. I have a black tank flush but don't see much point in overdoing it. I drain the tank, then use the black tank flush to refil about 1/2 way then drain again, at that point I'm done. It's not like I'm planning on drinking out of it.

I overfilled the Fresh tank one time and I guess I'm lucky I didn't damage anything.

[wagonmaster2]

How is the best way to find out if the vent pipe had dropped down into the tank? Would you have to use a mirror to actually see into the tank or if the vent pipe is still protruding from the roof would this indicate the pipe is still in place? With a wind directional attachment to the top of the vent pipe it doesn't seem likely the pipe could drop very far.

I guess the OP will be able to tell what happened if he has to replace his tank, but we can all hope he doesn't have to do that.

[sidney]

I leave the black tank valve open while using the black tank flush. At the same time I also pour a few 5 gallon buckets of water down the toilet to help rinse the tank.

[opnspaces]

Been there, done that also. In my case I was talking to the neighbor when the big boom happened. 😮 Tank split front to back. I also had a sprayer hose pop off, but that was more like a pop than a boom. Hope yours was a sprayer, but it most likely was a split. 😞

Throw away any fiberglass insulation that got wet as it's compromised. You can but some new pink stuff at Home Depot pretty cheaply for when the time comes.

As far as building pressure I'm not sure what causes that. But I do know based on the inspection I made during dis-assembly that the vent was not dropped into the tank and it was not plugged. I have always wondered if the noise was actually the sound of the tank splitting open under just the weight of the water in it. But then again I could swear that the trailer jumped a bit when the boom happened so who knows.

[NHIrish]

Lantley wrote:
Lesson to learn from all this is black tank does not need to be spotless.
Don't obsess over the cleanliness of the tank. It's ok to rinse it out but no matter what you do there will always be residual stuff.
Trying to get it spotless can create serious issues. Why get it spotless when all you are going to do is fill it up again?
I slowly learned myself, that obsessing over the black tank is counterproductive. A quick rinse or 2 and be done with it.
While I understand overfilling was an accident, there is no need to fill tank to the point of causing an issue. You should have quit filling long before the point of rupture. Quick rinses is all you need.
If you have odors use chemicals occasionally or as needed to eliminate odors.
Repeated long fills are unnecessary, Especially fills long enough to rupture tank.
Lastly you cannot trust tank monitors to determine fill level. Use a timer. Decide how long it takes to fill tank based on time. I never let my 40 gallon tank go longer than 5 minutes. Using a clear elbow I watch what comes out. Usually one or 2 rinses is all it takes. I also back wash black tank with gray water which works very well.
If it is not convenient I do not flush at all. If I am camping again in the near future I do not flush at all.
Once you get things back in order, I suggest you change to a less rigorous flush routine.
There is simply no need to take the risk of causing damage, think quick rinses vs. long fill ups.

And there's the truth. I do close the valve when using my tank flusher...no more than 60 seconds is my rule...which has worked for me.

[LakeN]

This thread reinforces my idea of sticking with Flush King for backwash. Have built in flush but once I saw the interior plumbing/potential for leak issues, decided to continue with trusty Flush King. Seems like it makes more sense for water to be entering tank at water exit point.

[BurbMan]

Same thing happened to me the first time I used the black tank flush...but my issue was that the PEX fitting going to the tank didn't have a clamp on it and it just blew apart. Once re-clamped all was good. Although my biggest problem is finding a dump station that will actually allow you to connect a hose that you can screw onto the rinse fitting.

[suprz]

I was thinking the same as the previous poster... Sounds like the black tank could not vent and the internal pressure made the tank rupture like an balloon

[Lantley]

Lesson to learn from all this is black tank does not need to be spotless.
Don't obsess over the cleanliness of the tank. It's ok to rinse it out but no matter what you do there will always be residual stuff.
Trying to get it spotless can create serious issues. Why get it spotless when all you are going to do is fill it up again?
I slowly learned myself, that obsessing over the black tank is counterproductive. A quick rinse or 2 and be done with it.
While I understand overfilling was an accident, there is no need to fill tank to the point of causing an issue. You should have quit filling long before the point of rupture. Quick rinses is all you need.
If you have odors use chemicals occasionally or as needed to eliminate odors.
Repeated long fills are unnecessary, Especially fills long enough to rupture tank.
Lastly you cannot trust tank monitors to determine fill level. Use a timer. Decide how long it takes to fill tank based on time. I never let my 40 gallon tank go longer than 5 minutes. Using a clear elbow I watch what comes out. Usually one or 2 rinses is all it takes. I also back wash black tank with gray water which works very well.
If it is not convenient I do not flush at all. If I am camping again in the near future I do not flush at all.
Once you get things back in order, I suggest you change to a less rigorous flush routine.
There is simply no need to take the risk of causing damage, think quick rinses vs. long fill ups.