No water - you dump with a slinky like everyone else - at the appropriate location. The Sewer Solution removes just like any other sewer connection and isn't connected by permanent electrical wires. Nothing to fail except possibly a seal, which could happen with any sewer connection.
As far as wasting water, It does take water to run it for a few minutes ( restricted to produce high pressure jet). But honestly, I don't believe anymore than someone rinsing out there tanks or using the open end of their water hose to rinse the slinky hose inside and out when done ( see it all the time). Unless someone has supported data of water consumption I don't buy that argument. Besides how any times have you walked by someone's camper where their water had a slow leak at the water connection somewhere and the ground was continuously wet.
Way too many other ways water is being wasted to make this an argument against IMHO. If someone was that worried about wasting water they should stay at parks where a old time out house with a hole in the ground could be used, problem solved.