A self-contained portable toilet that has a bowl which is mounted on a support bucket or holding tank. The bowl has an outlet port for discharging the contents of the bowl into the bucket, and a closure means for the outlet port is provided which comprises a flexible diaphragm movable between a first position in which it closes the port and a second position in which it uncovers the port. Means are provided to tension the diaphragm into contact with the outlet port when the diaphragm is in its first position so as to seal the port closed. A flush lever is provided for moving the diaphragm between its first and second positions. A flush water storage chamber is contained within the portable toilet and a hand pump is provided in association with the storage chamber for discharging flush water into the bowl.