A drain system for a tub of the type having a tub body defining a bathing cavity, a doorway with door sill in the tub body and a door in the doorway. The drain system comprises a drain piping section adapted to be in fluid communication with a tub drain hole in a bottom of the bathing cavity for drainage of bathing liquid therethrough. A drain unit is adapted to be connected to a door drain hole in the door sill for drainage of liquid therethrough. The drain unit has an inner cavity and a check valve held releasably captive in the inner cavity. The check valve is manually removable from an exposed surface of the door sill. A pipe connects the drain unit to the drain piping section to direct liquid collected by the drain unit to the drain piping section.