First, take a look under your bed. The mattress and plywood sheet lift up to reveal a storage area under there. You will also likely find your fresh water tank in there. I don't know why everybody specifies fresh water tank. I seriously doubt anybody has or uses a salt water tank! Anyway, once you've located your fresh water tank, you'll see at one end a largish hose that goes to a valve, then splits off with one side going to a pump. You'll want to fill your tank before turning the pump on, and ensure the valve is directing the water to the pump, otherwise, it'll be draining out under the camper.
On one wall, probably in the hallway near the bathroom will be a panel with buttons and lights to tell you how full your holding tanks are. You can ignore them. The switch for the pump should be on that panel, though. Once you have the tank full, the valve opened to the pump, and the switch on, you should hear the pump run until the system is pressurized. It will not properly pressurize until you get the air out of the lines, though. So start by opening the water valves at the sinks and tub until the water runs solid then turn them off.
Next, you'll want to turn your attention to the water heater. It may or may not have a bypass valve installed. It is also probably accessed under your bed. Ensure the plug is installed (it may have an anode attached) on the front of the water heater (outside). Then you can open the bypass valve inside if it needs to be opened. Back outside, you can open the pressure relief valve to let air out of the tank. When water starts coming out of the relief valve, close it. It is now safe to light the water heater if you wish. You'll probably want to wait until you are on site, otherwise, you're just wasting propane to heat water you aren't using.
Holding tanks - one grey and one black. When you look under your camper, probably near the water heater area, you'll see two valves. One is bigger than the other. One may even have a grey handle. The small one is the grey tank and the big one is the black tank. Keep them both closed while you are camping as long as you can. If the site provides sewer, then go ahead and connect up the stinky slinky, but leave the valves closed. When you get ready to leave, or the tanks are full, or you stop at a dumping station, open the black tank valve first and allow it to drain completely. You can also use your non-potable water hose with a wand to reach in through the toilet and flush the black tank some more. Once you're pretty sure you got all the solids out, go ahead and drain the grey water tank. This will serve to rinse the inside of your stinky slinky. Close the valves, remove the slinky, and cap the drain. You might want to invest in a box of nitrile gloves to wear whenever you perform this operation.
If you have no desire to travel with water in your potable water tank, turn off the pump (if it isn't off already) and switch the valve from the pump to the drain position.
Sanitizing the potable water tank is pretty easy, btw. Simply pour some bleach in the full tank, cycle it through all the faucets, then drain and refill. If you feel the need to drain and refill again to reduce the residual bleach, that's fine, but not really necessary.
Hope this helps!
2022 Keystone Cougar 24RDS
2023 Ram 6.7L Laramie Mega Cab