My old Prowler had a water tank gravity fill, that looked something like this:
You would pull out the trough and run water into it to fill the on-board fresh water tank. Your camper should have a 20 gallon fresh water tank. Do you know exactly which model camper you have?
Anyway, depending on the model, you should have a 12v water pump that draws off that tank. It supplies water to the toilet and faucet(s). You should also have a female garden hose fitting on the outside of the camper somewhere. That allows you to use a RV water hose, to supply fresh water. When you use the hose, you do not need to use the pump.
The waste dump should go to at least two tanks. A gray water tank and the black water (Toilet) tank. You basically let them get as full as you are comfortable with, then dump them at a dump station. Always dump the gray tank after you dump the black tank. That will help you flush any solids in the valve/hose.
Also... Always make sure you use enough water, when you flush the toilet... A lot of people don't use enough and end up with a "Black pyramid" in their tank... That's something you DO NOT
Please let us know exactly which model your Sunline is and we can help you a lot easier....