A waterless trap for use in a drain assembly includes flow enhancing features to promote the vortex water flow of water received in the trap, an improved sealing arrangement to enhance the seal between a seal member and the housing to inhibit sewer gas leaks from an attached drain pipe by maintaining an evaporation barrier that assists in retaining water in a corresponding p-trap, and a plurality of air passages can allow the trap seal to open with ease when the drain pipe is pressurized. These features may be used in combination with one another or may be independently employed.