[JoePeek]

What about the vent tube ? I'm thinking any pressure could not build up because of the vent. With that being said, running ATF with water in it would create less pressure on the apply pistons and there would be a lot of clutch slippage, not to mention the slippage that would happen in the torque converter. I would say drain out everything, replace the filter, refill with new fluid, let it run about 5 minutes. then drain it all out again and replace the filter again. After that, with new fluid and filter, drive it easy and see how it does. If it seems OK, repeat drain/filter one more time after maybe 50 miles of driving. If you are going to pay for dis-assembly to get the water out, you might as well just get it rebuilt.