here is how I do it. After I drop the pan, new filter and gasket, reinstall pan, fill the transmission. then I take the return cooler line off the transmission, put the open end into a bucket, Start the vehicle and put it into Neutral while a friend continously fills the transmission pan with ATF so that the pick up doesn't go dry. Once I see clean fluid coming out of the return line, transmission has been flushed, reassemble and check/fill transmission fluid. drive it around the block in all gears, recheck fluid level, fill if needed.
all in all it uses about 2 qrts of ATF in excess (lost during the "flush") IMHO, way cheaper than paying someone to power flush a transmission, which is not a good thing on an older transmission.
