Originally Posted by Jentine
It is not reasonable to pump everything into a tank, only to later discharge it overboard.
The pick-up for the overboard discharge pump is an additional line that would be plumbed into the overboard discharge below the Y valve.
I disagree. I think it is perfectly reasonable to pump everything into a tank and then out when desired. For several reasons:
1) This allow you to keep the seacock closed at all times except for the minute or two that you are watching it while pumping thus reducing the chance of a hose failure and leak.
2) The urge sometimes occurs when you are closer then 3 miles in and why have to think about changing the Y-valve setting when you really need to go.
3) Y-valves are a source of failure and maintenance
4) Having the Y-valve does not allow you to eliminate any other part of the system as you still have to have all the others unless you are comfortable using a pump-out all the time for your holding tank.
5) Not having a Y-valve allow the output hose from the toilet to have no connections all the way to the holding tank. This reduces the corresponding points of potential clogging hopefully reducing chances of failure.
6) Having a Y-valve usually means you have to locate it somewhere accessible which can just give you more hose to potentially leak, clog or break.
7) If you have the throughhull open while sailing it is prudent to have a siphon in the system to prevent backflow into the toilet which again just complicates the output hose of the toilet by creating a loop that holds sewage and increases potential smell and clogging.
Just my opinion. There may be other reasonable options but having the simplest system you can design should be included in with them.