I recently repaired a kitchen gray tank leak in my 2012 Montana 3150RL. I had a heck of a time finding the leak. It was apparently on an upper part of this 40 gallon tank because it only leaked when the tank was pretty full, near the drain. This tank is about 5’ x 2’ x 10”D, and runs side to side right above the dual axles with the drain on the left side of the camper. We spent the winter in Arizona so I decided to fill the tank and look for the leak because this would be a good place to dry it out afterwards. I filled the tank and I cut a flap at the drain to look for the leak. It was on the opposite side from where I thought! Water dribbles down to the low point near the drain (left front) when the tank is pretty full, and I found that the water was following the bottom of the tank to the low point (duh!). When I got a light into the belly and stuck my head in, I could see the water was leaking from somewhere near the front right corner.
I drained the tank and cut another flap (gulp!) on the opposite side and looked for the leak. I never would have found it if I didn’t know exactly where it was. This hairline crack is very hard to see, but when the tank is near full it must flex and the crack opens up. I found lots of useful info online on fixing it, and the best and most helpful were Ray Burr at “Love Your RV”
https://www.loveyourrv.com/repairing...h-plasti-mend/ and Bob ‘Montana Master’ Rohrman in the 5th entry of this thread
http://www.montanaowners.com/forums/...ad.php?t=72308 . My hairline crack was just like the ones that Ray experienced and in a similar position.
I decided to use Plasti-Mend since Ray and Bob both recommended it. I wanted to provide some support under the tank like Bob did because it seemed logical and Bob said the repair was successful with no recurrence, although Ray disagreed with the idea of altering the tank support design when I asked him by email. Planning and prepping this took more time than the actual patch, but I abandoned the idea because it was just too hard to do without dropping the entire Coroplast belly under the tank. I did the repair just as Ray did, and I had to unbolt a tank support beam to move it out of the way just like Ray. Everything went back together just fine when I reassembled it, although putting the beam back in place was physically hard because of the limited access.
Plasti-Mend is a serious product and I was very impressed with it. It costs more than the alternatives available at hardware stores, but I think it produces a much more sturdy and robust patch. It requires respiratory protection against organic solvent fumes, and I recommend eye protection also because I did the work while looking straight up. I used it exactly according to the directions, which I read many times. The patch for a crack is brushed on with mesh reinforcement, and the instructions say to go several inches beyond the crack, which was why I had to move aside the tank support beam even though the crack did not go under it. The patch is supposed to be stronger than the original tank wall.
When I closed up the Coroplast I used black Gorilla Tape “Tough & Wide” 2.88 inches wide, which was way better than some other Gorilla Tape that I had in my toolbox because it is extra wide. I also added another cross-beam directly below the tank, under the Coroplast. The Coroplast there was drooping a little because it had held the water leakage and also it is about 8 feet between cross-beams, so it seemed like Keystone should have put one there originally.
While I was underneath the camper I replaced most of the Tek screws holding the Coroplast up, using stainless steel screws and fender washers. Almost all of the screws in the front half of the camp came out after I loosened them with a ratchet wrench, but the screws in the rear half (from the axles backwards) all broke and had to be re-drilled. This replacement is a project, since there are about 100 screws total. In the back half of the camper I stopped trying to remove them and just drilled a replacement adjacent to any screw where the Coroplast seemed a little loose. In the rear of the camper there are some screws holding some sheet metal along with the Coroplast, which were loose and I re-drilled replacements.
I’ll test my gray tank repair next time we go camping and have hookups. I am crossing my fingers! Wish me luck!