Abstract: A flush system for a flush toilet in which an auxiliary tank is positioned in the main tank and which is operated according to a fluid pressure system. The auxiliary tank has a bottom wall which is spaced above the bottom of the main tank and has a fluid port on the bottom wall and a one-way valve in the top wall thereof. With the one-way valve closed, air can flow out of the auxiliary tank but cannot flow into the auxiliary tank. An air conduit is connected at one end thereof to a selector valve on the flush handle on the toilet and is fluidically connected to the auxiliary tank at the other end thereof. When the selector valve is opened, operation of the flush handle will permit air to flow into the auxiliary tank whereby water can flow out of the auxiliary tank during a flush cycle. However, if the selector valve is closed, the auxiliary tank is closed and air cannot flow into the auxiliary tank so water will not flow out of that tank during the flush cycle.