Thank you all for confirming what I thought.... I got the plate and plugged the other skimmer with a tennis ball, and got started. I had to stop before finishing because the vac seemed to lose suction and I suspected I'd filled the skimmer basket. I got the shallow end done, which wasn't bad compared to the deep end. I'm opening a pool that's been covered since October in New England, so it's BAD! I let the pool fill back up a day, and scooped as many leaves as possible out with a net, then let it all settle back down. I essentially had to start over in the shallow end, but this time I made it to the deep end and only have about 1/4 of the pool to go. Again, this session nearly filled my skimmer basket and I could hear the fitting at the skimmer plate sucking air because the water had dropped below (and it's like a 20 year old hose fitting with a small crack). I think if the pool were just needing a weekly "Tidy" then I could do it in one session, but this is like a recovery effort to get the pool swimmable before this weekend when it's 90 degrees.
Next question: I freaked out when I re-started my system after cleaning out the skimmer the first time, and switching back to filter. I had waited to have enough water, but the pump still needed to be primed, correct? I did it, but held my breath as the psi climbed up soooo slowly. The pump basket always had water in it, but the filter pressure started out around 10psi and hung out there a minute before starting to climb and spit water from the air release. Does this all sound normal? So each time I have to shut down to clean the skimmer basket, I need to prime the pump in Filter, re-establish suction on the hose, and then turn it all off, switch the multi-port to Waste, and then start vacuuming?
I'm grateful for my handed-down Polaris for the weekly cleaning!