holding tank replacement
I am also going to do this in the Fall. I got a complete procedure from Roy Mosteller (look him up on the owner directory in San Diego) with pictures and explanation. Contact him. He was happy to share his experiences. Ronco Plastics is the company that makes every size tank imaginable -- www.ronco-plastics.com -- Roy used the #B131 15 gallon size and cut through the aft bulkhead, because it is pretty difficult to go in through the lazarette standing on your head. He also replaced the old black hose with new OdorSafe Sealand Technology hose you can get a WM. Peggy Hall says to put all fittings on top of the tank if you have room (5" she says) to prevent odd leaks and backwash back into the toilet if your joker valve leaks. That means you probably need to have a dip tube that reaches down to near the bottom of the tank on your pump out port. Good luck. I am amazed that Hunter Marine put an aluminum holding tank in boats that would be used in salt water, especially when they used plastic for our diesel and fresh water tanks. Go figure.
