First you want to have about an 1/8 to a 1/4 fresh water in your tank. On my rig, you attach the hose and set the dials to city fill. Fill your fresh water then set your switches to normal setting. This setting enables you to use the on board pump in route. When you start you trip, make sure you have the pump switched to on so the toilet will flush and the spigots will work. You don't want to completely fill the fresh water if possible cause your adding 10 pounds per gallon weight. Before the trip, as others have said, hold down the flush on the toilet and get at least a couple inches of water in the black tank, and also add a bottle of Thetford waste emulsifier to it. Never let the black tank go dry at any time, even when parked between trips. Always at least 2 inches water and chemical. When the water and chemical are in there, the movement of the rig creates a washing machine action that helps scour the bottom of the tank clean. When you dump your tanks at the end of the trip, dump black tank first then grey tank.( I suppose that's obvious but figured I'd throw it in anyway). Then refill with 2 inches and chemical again. You have to manage that crapper right or big trouble
Have fun.