I have traced the waste hosing from the head to the holding tank to the macerator and then to the through hull.
I would like to install a y valve and by pass the holding tank for off shore use.
The only way I can see this being done is install the y valve before the holding tank.
The diameter of the through hull fitting that is currently being used from the macerator is to small.
I would think the only option is to add another through hull fitting for each head, that would mean drilling two holes in the hull to accomondate this.
Would anyone be able to suggest something different or a better way to do this.
Another question would be where would the proper locations on the hull be to drill a hole for each head.

The 400 already has way too many through-hulls. Too many possible points of failure for me. Mine had something like 15 or 16 with the AC and dual refrigeration. Why not just use the holding tank and dump it every 2 or 3 days while offshore? Run the motor if you're worried about amps. The only reason to not do it this way is to avoid using the holding tanks at all on a new boat. But once you do use it, you may as well use it all of the time. The damage was already done. Possibly do the last flush with water from the sink to get the saltwater out of the tubing.

If you really want to install a "Y" valve before the holding tank, I think you can divert it to the macerator through hull. I've seen many Catalina's modified this way. It should work unless they started putting in much smaller waste tubing and thru-hulls. I think mine were something like 1 1/2 inches or so (if memory is correct).

Ron M.
C400 #74 "Good Vibrations" (sold)