Took me about 6 hours just a few years ago to just change out the hoses that go from the through hull up to the Y valve, the Y valve, and the hose from the Y valve to the toilet. Honestly, if the door to the underside of the sink was double in size, it would have been a piece of cake, but getting that Y valve off that aft wall under the sink is terrible. Once that was off, it was easy to get the hoses off. taped up the ends and took them in to West Marine to make sure I was getting the exact hose. The reverse process to reinstall.