oops forgot to post this--
Rob, I used my overflow hose. I got a three-valve bag on Ty's recommendation (glad I did) so one of the valves was near the front of the bag on the top side. Since I used braid-reinforced hose it was stiff enough to push the bag into the locker.
Note that my locker has large-diameter PVC pipes running the length of the locker, and I'm assuming yours does too. Because I wanted the sides of the bag to lay on top of these pipes, I made sure to prep the bag carefully for insertion to the locker-- with the bag laying in the boat, I folded each of the long sides in a few times to make the bag skinnier going into the locker. Once I pushed the bag all the way in the locker I used a pole to unfold the bag edges over the tops of the locker pipes.
I never took the time to measure how much water or weight was actually getting in the locker once the bag was in there. I decided to trust that it was a good installation overall and to check the net result on the wake. Given the huge improvement in the wake with the bag filled, I'm honestly not real concerned whether it took 700lbs to get there or if I'm actually only netting 500-600lbs-- I just know I liked my wake before, and now I love it way more.
Send me a message if you need any help or more ideas.