A vacuum tank assembly has a low volume configuration so that it can be used in boats and recreational vehicles where space is at a premium. A stack of components, with a waste tank at the bottom, then a vacuum tank with directly connected vacuum pump, and one or more fresh water tanks, is located remote from a vacuum toilet, with a discharge from the toilet (below a vacuum-tight ball valve) connected to the vacuum tank, which is in turn connected to the vacuum pump, in turn connected to the waste tank. A submersible centrifugal pump may be provided mounted to a cap of the water tank, with an anti-siphon device associated with it. The vacuum tank is of high density polypropylene having flat walls, with no continuous flat surface more than 80 square inches. Lipless duckbill check valves are provided on opposite sides of the vacuum pump, the valves of elastomeric material having a ratio of the wall thickness to thickness of the sealing edges of about 1:1. The waste tank may have a dip tube with a dog leg portion having a large cross-sectional are oval bottom opening to minimize the possibility of clogging.