Re: WTF is this?
We can see that the three way valve would allow waste to be immediately dumped overboard or diverted in to the hidden holding tank. There is no deck pump-out, so I assume that the tank was emptied overboard when offshore. Hence the black box, which is, as some suspected, a holding tank alarm. When it went off the owner probably hove-to and manually pumped the waste overboard. Either way, removing this ancient artifact is going to be a lot more work than I first assumed....it's a boat, go figure...
1969 S&S Yankee Dolphin 24 "Avri Ellis"