Back in the dark ages, torque converters and fluid couplings could be disassembled and cleaned. Some converters also had drain plugs. It's possible to get more fluid out of a transmission by disconnecting one of the cooler lines at the radiator and running the engine to pump most of the fluid out, then refilling with fresh fluid. That's what some franchise shops call a "flush". As long as you don't let the pump run dry long enough to damage it from lack of lubrication, that's one way to pump most of the old fluid out. Some transmissions need to be shifted to "drive" to get the cooler circuit working.
Jerry
