Success! Hubby and I went back out and discovered that the mysterious clear glass with a lid right before the pump basket is actually something you pop off to get out debris. It opened right up, we cleaned out a huge amount of leaves, and followed our normal pump priming process using only the main drain and closing the skimmers. After about 5 frantic minutes, the main drain started flowing and I was able to SLOWLY open up the skimmer lines without losing prime. I guess I had a TON of air in the lines because the system had been trying to vacuum without good flow due to the leaves. Lesson learned: no vacuuming without a way to catch the leaves!