Why?

Well... same question. But of interest to note: my new F250 with the 4R100 Tranny has a drain plug in the tranny pan. https://www.f150online.com/f150board/smile.gif Should make change less messy huh?

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2000 F-250 Super Duty, Super Cab XLT, Oxford white with grey cloth captains chairs, 5.4L Triton V8(260 HP version!), 4R100 4 Speed Automatic Transmission, 4 wheel ABS, Deluxe Aluminum Wheels, Trailer Towing Package, Class IV Hitch, Reece load distribution system, Escort Sensor II Electronic Brake control, K&N filter, "White-White" head lamps.

That is handy.

trans fluid mini chg-t'ween Reg changes
 

If I wanted to replace (freshen) fluid in pan between regular fluid/filter changes, could I use a siphoning device to remove the 6 qts, or so, through the dip stick tube?

I guess, since I saw the clean filter and lack of "stuff" in the pan, I thought I could save the labor cost of the typical transmission svc. consisting of dropping the pan to drain and refilling the 6 qts. of fluid.

It would be easier and probably less messy to drop the pan and replace the filter than what you're talking about doing.

Yea. Why not just "do it all" once you are in there? Well if you really must do this then go ahead and get you one of those B&M aluminum extra capacity tranny pans with the drain plug already in it and replace the stock one so you can do what makes you happy. I think Summit has them. Not too expensive.

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2000 F-250 Super Duty, Super Cab XLT, Oxford white with grey cloth captains chairs, 5.4L Triton V8(260 HP version!), 4R100 4 Speed Automatic Transmission, 4 wheel ABS, Deluxe Aluminum Wheels, Trailer Towing Package, Class IV Hitch, Reece load distribution system, Escort Sensor II Electronic Brake control, K&N filter, "White-White" head lamps.