It's been a few years since I owned a V/P Duo-prop... But I used to remove the dipstick on top of the drive, then the shift linkage cover, and finally the plug you mentioned. Then I'd tilt the drive up and fill it through a funnel and long clear plastic hose. It takes a long time, due to the viscosity of the oil. I rigged my funnel to stay up with some plastice tie wraps so I could fill it, walk away and do something else, then come back and fill it again until it was full. Then I'd put the plug in, lower the drive, and top off the same way with the tube and funnel.
I have the same VP outdrive and use a small pump made by OMC (threads match) to fill the gear case. Requires removing the props. Screw in the pump fitting into the lower drain hole. Check dipstick while filling to avoid overfill. Tighten dipstick then remove pump fitting and very little will drain out before you insert the drain bolt. Filling through the dipstick is too slow and can trap air IMO. Good luck!
Why don't you pour the fluid in through the dipstick opening? I believe this is VP's recommended method, and the outdrive only uses ~2.5 qts. (or course I use fluid that comes with a tapered cap for ease of pouring). Or use a manual fluid pump -- one hose in the dipstick hole and one in your fluid bottle and pump away.
By the way -- I've seen the Snowwolfe down in Valdez -- nice boat!
I bought a simple pump for gear oil and changed it yesterday. I am lucky enough to have the boat parked on a gravel pad so I was able to remove enough gravel under the drive unit to lower it completely to aid draining. After filling it up I had to top it off a little by adding thru the dipstick hole. It would of taken hours to add 2 1/2 quarts via this method.
Thanks for those who offered advice.
By the way, the name of my boat is "Bite Me'. Snowwolfe is just my handle online
DreamCatcher, How are those new props working out?
Going form F5 to F4 prop raised rmp level slightly at my normal 22 know cruising speed. I was close to the recommended WOT range. The engine seems to run a little smoother (less load) so I'm glad I bit the bullet and swaped. Should anyone be interested, the F5's are for sale!