Peggie Hall,
I asume that you will see this message. I am a little worried about
trying to clarify your response after viewing the responses tacked
onto my initial post.
If you would please review my configuration from my initial post. This
boat (since 1980) has always been configured: head to vented loop to y
valve directional to either holding tank or thru hull. The vented loop
is well above the water line, I have never had to close the thru hull
when sailing (with the y valve directed toilet/thru hull). I
understand that the vented loop is not necessary between the head and
holding tank, but it certainly does no damage, and the plumbing is
already in place.. To do what you recommend requires quite a lot of re-
routing and a heck of a lot of labor. Why would I lower the vented
loop down by the thru hull, necessitating the requirement to sail with
the thru hull closed? I simply believe that injecting the macerator
discharge into a "T" between the head and vented loop (with a ball
valve between the "T" and toilet to prevent backflow into the head
when operating the macerator) would be a much easier endeavor than
anything else.