I have a 2014 3600 and there are 3 tanks/handles. 1 for the gally grey tank, one for the bathroom grey tank and one for the black tank. Since this is a Front Living, my guess is the handles for the Bathroom grey and black tanks are in another location rather then up in the UDC. Looking at pictures of the 3091 it looks like your sewer connection is behind the axles which is not the case on the other Sanibel models, they are all pretty close to the Docking Center. I would peak around the sewer connection, I bet you will find the handles for the bathroom grey and black tanks.
As for the couches I just lift up the seat cushions and its a fold out bed, just lift up and the bed starts to unfold like a normal hide a bed couch at home.