Found the plug, Chris. It's on the pot and for some reason I never thought of the pot as part of the pump but in looking at it closely, it clearly is. No leak there, though.

I pointed my husband to this thread and he wrote back that "we'll be doing some detective work this weekend."

The hose I use for manual vacuuming has two white ends and neither swivels. It's the same kind of hose I have attached to the filter for when I backwash/rinse. I'm guessing this is not a vacuum hose then?

Thanks for working with me on this. I'll post if/when we find the cul[rit air leak.