HOPEFULLY this is what happened...
there is a flexible rubber sleeve connecting the wash tank pipe to the black Y pipe...
one leg of the Y is from wash water and one leg is from the black tank.
since the tanks move a bit there is a ~6 inch sleeve
and 2 screw/ring/hose clamps used to attach tanks to the Y...
((very much like plumbers use in household low pressure sewer drains))
either might have been blown off, but IF it's the black tank the LEAK should smell different...
u really can't KNOW for sure without looking at BOTH legs of the Y
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it IS possible to visually access the Y without dropping the flat belly pan...
but getting TO the clamps and rubber sleeve are really hard with the belly pan in place.
the tanks are PARTIALLY/significantly supported by the pan,
so it cannot simply be DROPPED (without supporting the tanks) and it will be IN the way once lowered.
it is much EASIER to cut a HOLE in the pan (keep enlarging the hole as needed) near the Y pipe...
then cover it with an aluminum or galvanized patch and stainless screws afterward.
just to add to the challenge,
the SCREW head for the large hose clamp/s is often oriented UPward, 180 degrees from access ...
which means a BENT screw driver (or nut driver) is needed to loosen it...
THIS can be a field repair and doesn't require any really special tools...
(metal snips, funky screw/nut driver, a couple of BRITE lites, goggles, gloves an extra hose clamp, and so on...)
but it is a tight space and RAISING the street side tires on a ramp helps provide space to work ...
once the rubber sleeve is slipped back ON and hose clamps secured,
TEST both tanks and all connections before closing the hole...
lower the trailer back to level 4 this test/inspection
and fill both tanks with water, empty each and LOOK for water at the connections.
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i'd post pictures of the actual repair,
but didn't wanna get the camera wet at the time i made this fix...
the images are burned into me'brain...
cheers
2air'