Hi: Well, you have a job on your hands to find and repair the leak. There are many possibilities for the leak you see. A drip from the tank metal pan means you gotta do some experiments. What situation causes the drip? Try to narrow it down.
Empty the tanks completely. The leak goes away, right?
Put a little water in the grey tank first from the shower. Maybe an inch or maybe 15% full. Observe leaking? If so, the leak is maybe from the shower drain plumbing or at the bottom of the grey tank.
Put a little more water in the grey tank from the vanity sink. Observe leaking?
If so, the leak is maybe from the vanity sink drain plumbing or a bit higher up in the grey tank.
Put a little more water in the grey tank from the galley sink. Observe leaking? If so the leak is maybe from the galley sink plumbing or even higher up the grey tank.
Observe the dump valve connection to the grey tank. It is likely held tight to the tank with a hose clamp. Look for leaking in this area. It is the lowest spot on the tank. I had a leak in this area.
Drain the grey tank. If you still have no idea where the leak may be coming from, start testing the black tank in the same manner. Only the toilet fills the black tank, but see if you get a drip from a little water in the black tank, or a lot of water.
Polyethylene holding tanks can be repaired with a special type of epoxy or by doing a "weld" of the leaking area. It is a big dirty job to remove the pan around the tanks, and then disconnect drain plumbing and remove the tanks. Big job. I don't know your year or model of trailer. I don't have a faceboo account.
Here are a couple of photos of the tanks in my 75 Overlander and my friend's 76 Sovereign