Success but not easy. I finally found a way by balancing on the seat on my stomach to get at the thing. I couldn't get it to twist off. After many tries thought I'd see what the latch 1/3 from top did. I thought it was what held it in place on the boats body. I could see nothing. Anyway, undid it and twisted again and it came right off! By the way, I didn't mention that this boats always in the water in the dock. The thing I wasn't considering, that happened, was as I pulled the cartridge out, water started pouring in. So that made me pretty nervous. I expected the cartridge to be all rusted out and frozen but it turned easily. Regardless, just knew I had to get it back in quick and hope the water would stop. Luckily I got it stuck in and turned. Then tried it and it worked! I was expecting to replace the cartridge like I did the bilge pump so that was great. Now I know I'll have to get the boat out if I have to do that again. Thanks!