I have a 1975 Cat 27. It has never had a holding tank for the head. It's all disconnected and the bowl is just a shelf in a closet. I plan to put the tank under the V-berth. I would like to know where I can find a quality tank that will fit in the center of the hull under the V-berth. I have read some of the articles by Peggy and I agree with them. All the tanks I have seen are not quite the right shape and have a very small single vent hole. I need to keep the tank as low as I can so the out flow from the bowl is down hill. So I know the tank will need to be some kind of wedge shape. I am sure somebody has installed a tank in this location on the same model boat, there are lots of Cat 27's out there. Any suggestions would be great.