Thanks. Yea, I'm the one who overtightened it because it was leaking so I figured it wasn't tight enough. It shouldn't be worn because it's brand new, but maybe I damaged the gasket by tightening it so hard. The 2x4 probably won't work as the handle is made to grip underneath with your fingers.

Loosen it slightly while pump is running goes against everything I've previously heard, but may be my only option. I'll be sure to keep my face clear of it's path in case I loosen it more than slightly by mistake.