Y - valves

[K2MSmith]

I’m trying to understand how these “Y”
valves work in my crazy head / waste system which is plumbed with 2 y valves . Which direction does the flow go ? One valve has a broken handle . I always thought the flow is in line with handle but these valves have “flow” and “open” labels on the ports .

 

[Loren Beach]

It's been at least a decade since I rebuilt and reformatted our boat's head system. I replaced the old RCMarine (nowadays Forespar) valve with these Bosworth valves. They still turn freely.

Sea-lect® Diverter Valves | West Marine

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[K2MSmith]

These valves appear to be made by "Five Oceans" according to some quick internet searches on images that I made. They are cheap and probably should all be replaced.
The waste plumbing is very weird and I don't really understand it (see sketch ) . I'm guessing the multiple Y- valves allow the head to go directly out to the ocean if so desired. the Simplest installation might be just to block off one of the two tank outflows (the one that is not connected to the deck fitting) and connect the toilet directly to the inflow. I don't see myself dumping the tanks at sea in the near future...

 

[Christian Williams]

Same brand. This drove me nuts and I had the valve wrong all the way to Hawaii, which filled my holding tank with sea water.

It was impossible by the design of the valve to confirm "which way" the flow went (and it was installed upsidedown and invisible).

So at least you have company. And, yeah, I don't remember the answer .