Gray Tank leaks when full

Years ago I owned a trailer that had a broken tank at the inlet. I cleaned the top of the tank and put layers of roofing "Eternal Bond" tape around the inlet without removing the tank or the pipe.

Afterwards, I was careful that the tank was never allowed to overflow to test the water tightness of my repair. My main concern was that I sealed the area where a foul odor was entering the trailer.

A portable tank is a good investment to make sure none of the tanks ever get completely full, or over full.

I've had two tank leaks. BOTH were along the bottom edge (Grey) and or the dump outlets (Black). Both due to overfilling at least once.
Plastimend fixed both successfully. No need to drop the tanks, just the underbelly covering. Leaks were very visible after the belly was dropped.

I also have same problem with the black tank. To drop the tank is going to be a big deal of a job. Then "if" I can see and repair the problem I have to get it back and keep that seal in place. The factory screwed it so I'm thinking so also will I !!
Was wondering about that spray seal you see that guy on TV using to seal a lot of things, even a screen door used for the bottom of a boat. Will have to get at it from the top. What I can see is they cut a 4" hole for a 2" pipe, so pushing the insulation back with my fingers and a stick and spraying that stop leak over a period of a full day or 2, little at a time so it runs down the pipe, across and around the joint and top of tank, hopefully, as it will be a blind job. Not the right way, but if it works. Then if you ever have to remove the tank, one would need to cut the pipe above the floor and use a rubber coupler to put it back together, which will be the proper way as I see it and seal the heck out of that pipe to tank while it is sitting on your work bench. Saying all this as I "think" my leak is from the vent line input. If it is the toilet down pipe input to the tank I will not be able to get at it without cutting the floor away inside the wall and spraying from that point. Problem is with the tank top all cruddy and dirty now, will that stuff ever stick as that plastic is very hard to get something to bond to as it is.

Allworth wrote:
Agree with the analysis; don't agree with the solution.

Leave the valve closed and then empty the tank when it gets to 3/4 or when you empty the black tank. (You do know, don't you, that you should empty the black tank first then empty the grey to flush out the lines and hoses?)

Agreed. Also, if you are handy, improve the DWV connections. Mine does the same thing. When my michigan driveway is clear of snow, we will return north and this is just one task I need yo address.

Our Grey tank on our Montana also leaks only when full. Will let the next owner decide if they want to fix it or not. Meanwhile, we don't let it get full. Montana passed it on to us which seems to be acceptable so we will pass it on to the next owner.

shovelhead86 wrote:
My gray tank leaks when full. I haven't removed the bottom enclosure yet but will on the next nice day. What can I expect to find. I have a 2007 Montana 3475.

It is NOT normal in any way. You have a split in the tank or it has separated at the inlet.More likely at the inlet. You will not be able to see a separation at the inlet.

You are luckier than us. Ours was the black tank. What a mess. Now we dump every four days and we did use an entire tube of chalk to seal where the down pipe enters the tank.

Yes, I know to dump the grey after the black. It never leaked in the past even when the tank was so full that water was standing in the tub. It started last week. Thanks for the info.

Agree with the analysis; don't agree with the solution.

Leave the valve closed and then empty the tank when it gets to 3/4 or when you empty the black tank. (You do know, don't you, that you should empty the black tank first then empty the grey to flush out the lines and hoses?)

You will find that the PVC stub, that your rubber flex line is connected to, is only held in the tank with a grommet. When your tank is full, water leaks out around that grommet.

Leave your gray water valves open unless you are dry camping.