I am assuming you are trying to flush it out. You cant get all the fluid out of the converter without removing the converter but you can have the tranny flushed out which is the next best thing to do. Remember to flush it with Toyota tranny fluid.
there is a machine that goes inline with the tranny cooler lines. As the old fluid pass through the machine, it drains it out and is replaced with the same amount of new fluid. It is done with the car running and in gear. It will replace appox. 95% of the fluid. It costs more than a "regular" trans service, but worth it in a car that is driven hard. Normal service will only replace appox 30% of the old fluid. Toyota recomends you do a trans sevice at 30K. If I drove an auto, I would flush it every 30k instead just due to the load the tranny is under. Hope this helps-