Hose connection question

[JohnGleadle]

I have four throughulls in my engine room and I just repurposed one for my watermaker. The others are engine, generator, and aft head. I need to add the salt water pickup for my sink/anchor washdown to one of these throughulls. Rather than adding another hole in my boat by installing another throughull, I would like some alternative ideas on how to do it.
I can add a T, or a Y to the watermaker or head line - that's the easiest but what stops pulling water from the inboard area rather than the seacock? And is there a problem with cross contamination?
I have heard about using less throughulls and drawing off an inboard reservoir?
How does this prevent the problems discussed above?
I can use one way valves but do they add restrictions to the flow?
Anyone have any experience with doing this project?

[Cavalier]

Originally Posted by JohnGleadle

I have four throughulls in my engine room and I just repurposed one for my watermaker. The others are engine, generator, and aft head. I need to add the salt water pickup for my sink/anchor washdown to one of these throughulls. Rather than adding another hole in my boat by installing another throughull, I would like some alternative ideas on how to do it.
I can add a T, or a Y to the watermaker or head line - that's the easiest but what stops pulling water from the inboard area rather than the seacock? And is there a problem with cross contamination?
I have heard about using less throughulls and drawing off an inboard reservoir?
How does this prevent the problems discussed above?
I can use one way valves but do they add restrictions to the flow?
Anyone have any experience with doing this project?

If at all possible, I would avoid any dual use of the engine or watermaker intakes - as you wouldn't want to cause any flow issues with those.

I'd run a Tee off the aft-head intake downstream of the seacock. I doubt you're going to be concerned with any cross-contamination between the heads inlet and the wash-down pump. If you're concerned about cross-contamination, you could always put a check-valve in the heads-inlet downstream of the Tee to ensure that fluid can't be pulled into the wash-down pump, however flow is more likely to come from the unrestricted through-hull.

The majority of check-valves are sized such that there isn't a reduction in cross-sectional flow area, which is why the bodies of the valves are quiet large compared to the line-size.

Hope this helps.

[Blue Stocking]

My foredeck washdown is supplied from my forward head tee'd thruhull, with a clapper type non-return, It has never affected the head. Its volume easily overcomes the vented loop pick-up for the head.

[a64pilot]

Apparently both my heads have drawn off the engine's seacock, and have done so for 27 yrs with no issue, and no check valves of any kind.
I'm installing a second AC and have planned on Ting into the fwd head's supply line, that would make one engine, two heads and one AC pulling from one seacock. Fewer holes in my boat, the better.
Oh, and check valves are things that stick in my experience