If the photo is upside down--iow, those fittings are actually in the top of the tank--the round one is most likely the sending unit for a waste tank level indicator. There should be a light panel in the head that indicates the level in the tank and has the brand name on it. It may or may not still be working, though.
The writing on the white hose says "potable water and sanitation," which can either be the hose from the toilet or hose that it goes to the deck pumpout fitting. If it's the pumpout line, there'll be a pickup tube (hopefully NOT metal!) on it inside the tank that goes to the bottom. The gray fitting appears to be a reducing adapter, which would make that hose the inlet from the toilet. I have no idea what the rectangular panel next to it is or why it's there.
The tank appears to be fiberglass...and that somebody just glassed in the hose connections instead of installing proper fittings for thread-barb hose fittings. They also failed to double clamp the hose connections.
You should be able to trace both hoses to find out what's at the other end of 'em and you need to do that before using the toilet which, judging from what I'm seeing at the tank, may need work too...and the tank may or may not be empty.