Lost head pressure

[Celtic_Wind]

We have a manual Raritan PHii which we recently rebuilt, after much cussing and a few scraped knuckles. Things were flowing good, great water pressure coming in, there was much happiness in headville.
Then a few days ago the water flowing in seemed to be less and we could hear gurgling from the head sink while pumping, obviously sucking air through the sink drain, (the sink drain uses the same thru-hull). The head still works, but with much less water entering with each pump stroke.
I've closed off the thru-hull and filled the sink with water and it seems to pump pretty good that way.
Before I tear into the thing, any thoughts on what has happened? Could there be some blockage in the end of the thru-hull, (the thru-hull opens and closes fine)? Our diver is coming this week, so we may find out more after a cleaning.
Other ideas?

 

[Mark Maulden]

Is this boat new to you? Sounds like a PO followed Peggies advice and teed the sink drain into the toilet input. If you close the thru hull and fill the sink with water, it rinses out the whole toilet with fresh water which is what should be done when leaving the boat. With thru hull open, put the sink plug in and it should work normally..

 

[Peggie Hall HeadMistress]

I've closed off the thru-hull and filled the sink with water and it seems to pump pretty good that way.

That seems to rule out any problem with the toilet. If it's worked fine till now, I'm guessing that your sink drain/head intake thru-hull may not still be completely below waterline. Water and fuel tanks weigh a lot more--8.33 lbs/gal for water, 7.5 lbs/gal for diesel--when full than when empty...are there any water or fuel tanks on that side that may be a lot emptier than they were? Or have have you added any weight to the other side? If none of the above, what happens when you just plug the sink?

 

[Ron20324]

[QUOTE="...your sink drain/head intake thru-hull may not still be completely below waterline. ?[/QUOTE]
+1.
This was the problem when I TEE'd the sink drain for the head intake on m B323. It would hardly pump any water without plugging the sink drain. I calculated how much I could cut off the thru-hull, then did so. It maybe 3/8 inch. It can still suck some air from the sink , but there is enough water to do a flush. As before, plugging the sink solved the problem,