Pat, are you absolutely sure that it is the tank?
A cracked fitting, loose hose clamp, pinched hose, or even a leaking pump could empty your tank in a weekend. This spring, the tank on my 25 emptied twice before I found that the functioning pump was leaking like a... bad pump. It worked but it leaked. It leaked harder when it was on. The rebuild kit was 2/3's the price of anew pump so I opted for the new pump. I would do some testing before I got into to that. However, It couldn't hurt removing it just to clean and inspect it. I did that with my tank three years ago.I hope you find the leak!r.w.landau