The drain plugs are usually at the back of the transmission, but may be near the rear tires. My B8200 has 2 of them, but only one needs to be removed for proper drain of the tranny/3pt (it is just one big hydraulic reservoir). I can't remember on the B7100 if you need to remove both of the lower drain plugs to get all the oil out. I'm also not sure of the exact quantity of oil, but it is likely around 3 gallons. I just buy a 5 gallon pail when I change my fluid. The fill port is located on top of the transmission housing, probably under the seat on your model, it is near the dipstick.
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