Abstract: A simple, lightweight device for the automatic flushing of a toilet which works on the principle of displaced air is disclosed. An air bag disposed between the seat and the rim of the toilet bowl communicates with a bellows vertically disposed within the flush tank. A shaft depending from said bellows rises and falls with the contraction and expansion thereof. An angled member pivotally attached to said shaft is caused to rotate by guide means in one direction as the shaft falls, and in the other direction as the shaft rises. In so doing, it first engages, then unseats, then releases the flush tank drain valve apparatus.