Jim and Jane
..sorry you didn't get a response the first time. I would call Hunter customer service who can give you advise. However, as a Hunter 40.5 owner, I had several. In the aft, the tank is a large poly sitting on a shelf. It apparently leaked a couple of times but I could not figure put the source. Finally, I realized that filling it up all the way was the problem. So, it is at a top fitting, inlet or vent. I now leave about 2" below the top. No more problems, even under 20 degrees heel for a long time. (I know, I know, I should reef...) Also, on the 40.5, there are two tanks under the cabin sole. They are intregal with the hull liner. They have a glass top that screws on to the tank. Over time, with normal hull flex, they seep, causing damage to the sole if not repaired. For mine, I have found simply bedding the screws again has fixed the problem. However, in any case do not pressurize the tanks when you fill them. Drain enough water out of each to empty the filler hose and take the pressure off the lids. Just run the water a while from each tank. Good luck. Maybe someone can give you a better reply. Rick D.