An update on my black water tank leak:
In another thread, I forgot which one, I thought the leak was in the black water drain valve, which I replaced, and it is now not leaking and it works smoothly. BUT - I found a couple days ago that my tank was leaking around the pipe collar as it enters the tank, at the top of the seam as was reported at the beginning of this thread. This seems a fairly common problem, and I agree with others that it is caused by the flexing of the pipe at that point against the tank wall.
The problem, as I see it, is that the tank is not particularly rigid and there is too much "give" at that seam, weakening it. I repaired my newfound leak using multiple layers of fiberglass and black ABS plastic glue just like others have done in this thread. This stuff dries to a fairly rigid state and the fiberglass adds additional strength.
I also found an ABS cleaner/glue "spray" at Home Depot that I sprayed into the crack before I applied the fiberglass/ABS glue patches, and I feel this should have reduced the seepage that was happening under the old glue joint.
I have a metal "guard" under the drain pipes and I added a metal shim to it that now contacts the drain which should help to prevent some of the up and down movement of the black (and gray) water tank drain pipes.
I'm leaving on a camping trip tomorrow so will see how this holds up. When I get back, I'll look into a more secure and permanent support for the drain pipes - something like that was shown in an earlier post in this thread.
If I come up with something that seems promising, that might work on other trailers, I'll post pictures.
- Jack