Last summer I noticed the gray-water tank on our trailer was seeping from
numerous places. It appears that over the years, it had been damaged by the
effects of pulling it over gravel roads. The tank is exposed on the bottom
with no sort of covering or protection. I think it is made of polyethylene,
which is apparently a difficult material to find patching for. There are
people who weld it, or I could provide the specs for the tank and have a
new one made up, but I thought I would (characteristically) try something
cheaper first. I used some stuff called Seal-all which is sort of a general
purpose patching stuff which, according to the package, can even be used
on gas tanks.
It stopped the leaks
last season, but I haven't checked yet to find whether
it is still effective. I think I will look at making up some sort of cover
for the tank to protect it from the gravel.
If you don't get more appropriate responses, you might try the Seal-all
before you replace your tank.