A standard water-flush toilet has an upwardly open bowl provided with a seat for the user. Waste is carried off from inside the bowl by a flush using at least several liters of water.
In many situations such a water flush is not possible. This is the case in regions where water is in very short supply, in applications where the weight of the flush water cannot be managed (such as on moving vehicles, e.g aircraft), and where the toilet is only needed for temporary use and a water hookup is not available.
A standard waterless toilet uses a liner tube or bag, and is described in U.S. Pat. Nos. 3,619,822 and 6,052,842. Such toilets have a holder below and outside the bowl for a large-diameter tube of stretchable plastic, e.g. polyethylene. The tube is guided up and over the seat, then down into the bowl and out through an opening at the bottom of the bowl. Spreaders are provided inside the bowl to hold the tube open below the seat, and other guides pinch the bag shut at the bottom of the bowl above the opening. The-user thus sits on the bag where it passes over the seat and waste drops into the section of tube underneath the seat. After use the waste-containing section and tube part atop the seat is pulled downward and pinched of to seal in the waste and provide a fresh seating surface for the next user.
Such a system is fairly effective, but is complex and requires the use of a fairly expensive toilet system. furthermore the disposable bag-forming tube is quite expensive also.