Someone may come along with the same model as you and very likely can tell what drains into which tank. Not always the case! My main bath goes into 1 gray tank, the kitchen and 1/2 bath sink into the other. Each bath has it's own black tank. The clothes washer dumps into the 1/2 bath black on my 5er and the same model owned by another it dumps into the gray.
1st I'd do is get the sewer adapter that has a hose connection and try back flushing. The Amish Craftsman that cut the hole in that tank may have left the cutout piece in the tank. Now it is a blockage.
EDIT ~ your edit and my post at the same time.
__________________
2022.Montana 3855 BR
2019 F350 6.7 4X4 DRW
|