Until you pull the membrane down, you can speculate on many possibilities.
I would pull the membrane, look for structural support for each tank, drop if necessary to repair. Many tanks with drain lines use no hubs as connectors and may simply need to be reattached, once the tanks are secured.
When that happened to me, I used "weather shade" as a new membrane as pulling back the original together is almost impossible.
Bob and Better Half
2007 F-250 PSD, SW, CC, LB, 2WD
2006 TF32SS Cross Terrain Toy Hauler (sold)
Reese 16k slider