Hello all.  Looking to validate something on my 1995 c36 mk ii, hull 1433. I've read some articles on the sending unit. I have a aluminum tank. I have noticed the access port for the fuel shut off valve, but never noticed one for the sending unit. If I have to cut a hole and install an access port, what would be a good size to get?  Also, where would the sending unit be. mounted?

Also, want to validate the tank size if I need a new sending unit.  The sending units on catalina direct shows one for a 25 gal and another for a 19 gal tank. Everything I have read says it's a 22 gal tank. 

My gauge has been having problems. First, the gauge went far left when the tank is full. Once it dropped to about 3/4, it would read correctly. Now it's not reading any fuel level. When I turn the key on, the gauge moves far left. When I turn the key off, the gauge relaxes back to its resting position, a few mm to the right of "e". So I can actually see the gauge ping hard left when I turn the key on. 

I want to troubleshoot this weekend. So if I need to install an access port, I want to get it before I go to the boat. 

Thanks for for all your help in the past and future.