Winnie has a built in sewage tank which works wonderfully well providing the dump station is in the ground. It's gravity fed, not pumped. You just attach a bayonet hose, open the grate on the sewer, put the other end of the hose down the hole, pull the lever and the tank empties. All wonderful. Except on sites when the chemical waste dumping station is built above ground level. Then it doesn't work. So what do you do? Assuming your toilets are not cassettes.