I just did this, both the v-drive & transmission in my 2002 Sanger v210. MY Walters V-drive is Model 26D. There should be a description plate on the port side of the front of the v-drive unit facing the bow (see pics). This plate will tell you the Walters model # and, on mine, tells what type of oil to use. In my case, straight 30wt oil. The type of oil per model is also outlined in the manual.
My model contains 2 pints of oil. I could not pump out nearly this much through the dipstick or filler top of the v-drive unit. (Looking at the schematic, I think some gearing gets in the way of the pump tube hitting the bottom). So, I used the drain plug located on the bottom of the unit, port side as Tige Mike notes.
I have the complete v-drive manual (pdf) that I can send you but it's big at 10MB's. PM me with an e-mail address that can handle attachments that size & I'll be glad to send it to you or break it into parts.
My transmission, one step from the v-drive closer to the stern of the boat with red dipstick on the starboard side, takes AFT III fluid per the Mercruiser 350 MAG manual (which I also have pdf if you need it). I simply pumped out the existing and re-filled with the amount per the manual and then checked by dipstick.
It's an easy deal. Good luck & have fun with it!