Hi - I'm a new owner of a Gravity 3340. We love the trailer but we received no manuals. I am having trouble understanding the grey and black tank drain handles. I have 3 - 2 near the front, and one in back. I only have 1 bathroom. I seem to get get sewage from 2 of the three handles and the stickers on the RV are not clear. Also, the bottom is closed up so I cant really see where the tanks or the plumbing is.

I *think* the handles are -

front most handle - black
middle handle (next to the first in the front of the camper) - grey
back handle - grey

Is this the case? Why do I see sewage from the back handle? What drains go to what tanks?

Unfortunately, the handles for all of my waste tanks were left open by the dealer on my first trip, so I think some sewage got up into the grey tanks . Any thoughts on how to flush those?