Advice needed for combining thru hulls.

[SpaceRnglr]

My 44 foot boat Elessar wins the medal for most sinks (8 sinks total) and gets close with number of toilets (3 toilets). Needless to say she has a lot of thru hulls. None of the 13 seacocks are currently working and they will all be replaced during a haul out starting on 6 July (if she doesn't sink first, touch wood). I am considering removing 2 seacocks as follows and would appreciate any feedback:

1) the 2 sinks in the rear cabins currently join to one thru hull via a ~2m hose. I am considering linking the head sink to the same thruhull. This would get rid of one seacock in the under sink cabinet where access is very poor. Is 3 sinks draining into one thruhull a bad idea?

2) the other head sink also has its own seacock with very poor access. The only place I could combine it is the head intake and I understand I would need to install a ball valve to prevent back flow. My concern is that most guests won't know the valve exists and will flush the toilet per normal. My question--what happens if someone forgets to close the valve and pulls all the water out of the sink? Has anyone come up with a clever solution to dummy proof this? The head supply is 3/4 inch whereas all the sink drains are 1 1/4 inch. Would the smaller size cause a problem?

The crew cabin has its own head I plan to remove completely so that will allow me to seal up the drain thruhull. I need to keep the crew cabin head supply and sink drain for the water maker.

I have attached the original as built layout that is a bit hard to read but gives the basic idea.

Thanks in advance for any feedback.

[msponer]

Hi,
Have you thought of a grey water system with a pump?

I hate ours for the kitchen sink. It clogs easily. I've been meaning to give the kitchen sink it's own pump. But it works wonderfully for our three showers, bathtub, and three other sinks -- we have one pump (and thru hull) for all of that. We've found the Sealand waste diaphragm pumps to be super reliable, so much so that we've standardized on them for our dry bilge pumps. A version of it is sold with a float switch and collector box, as a single unit grey water system.

On another boat we had another style of pump directly underneath the sink. We would drain the sink by flicking a switch to turn on the pump. This worked well because otherwise the sink would backflood when we were heeled. Maybe if the angles don't work to combine your three sinks to one thru hull that drains with gravity, you could do the same thing, with three pumps output to a single thru hull. Maybe that's a little silly and a single collector box and grey water system would be better.

I don't have any experience with multiple sinks running to a singe thru hull, without a pump. Would the angles be such that a sink is down hill of the thru hull (or other sinks) when the boat is heeled? That's the only problem I can imagine. So maybe the three aft sinks you reference could be combined with a pump.

[SpaceRnglr]

I had thought combining the sink drain with the showers as they currently drain to the bilge. I thought I could rely on the bilge pump to get the sink, shower and bilge water out. After thinking about this some more that part of the bilge has some oil from the engine, combine that with hair = yuck. I eventually need to separate that drain area to engine bilge and separate shower drain area.

That said, showering in the tiny head in the Singapore heat sounds like torture.
I don't think we will ever use those showers (plus there is a deck hose on the swim platform) so this can wait a very long time. As a result I want to save this project until I have the other 9,999 projects done...

So all in all this option is tempting but not for now...