A contaminant-flushing machine for removing contaminants from a container, such as an engine transmission, air-conditioner coil, or transmission cooler, which includes hoses for coupling to the transmission cooler and a pump for circulating fluid through the hoses and the transmission cooler, and a fluid filter having a reduced tendency towards causing vaporization of the fluid. Also included in the contaminant-flushing machine is an automatic aeration system for injecting air into the circulating fluid at predetermined intervals. Additionally, a reverse flow piping circuit is included to permit automatic and electric manipulation of the flow direction of fluid through said transmission cooler while at the same time not altering the direction of flow of fluid through the pump. The flow reversals are repeated with a cycle of three (3) seconds in one direction followed by a flow in the other direction of one-fourth (1/4) of a second, thereby creating an overall flow of fluid primarily in one reverse direction. The bursts of air are less than one (1) second and occur at five (5) second intervals.