Bladder was original
My 1981 H33 had a bladder style holding tank that held about 10 to 15 gallons (I think). It was starting to stink like crazy, so I replaced it with a solid plastic tank bought at West marine. I first measured the opening to the storage area under the starboard cockpit seat. I then looked to see what was available, and made a cardboard mock-up to check for fit. It has been a couple years, but I think it was a 15 gallon tank. I installed it in the same area as the bladder, but secured to the flooring with straps. The only problem now is that it severly restricts my getting into that area to work on the stuffing box, of accessing the transmission. What I do then is to loosen the starps with the tank empty, and slide it over as far as possible to give me room. There was a post some time ago where somebody installed a similar tank suspended in the area behind the hot water heater. You might look in the HOW archives. Good luck.Ken Palmer, S/V Liberty