Originally Posted by caltexflanc
You want to avoid "uphill" as much as possible. We do have a true industry guru who frequents this site, so hopefully she will chime in. But the described routing has me puzzled. Are there boats really designed that way?
Thanks for your thoughts. I will add a post below and try to attach a picture that might help. The guest head is on the port side of the boat. Holding tank is to starboard. Waste route goes under companionway sole between galley and dinette areas, then to the holding tank after passing through a bulkhead to get to the engine room area.
As far as avoiding uphill, the top of the holding tank is for sure lower than the vented loop, or a Y-valve. The top of the tank and the top of the toilet are about the same height, but of course the vented loop or Y-valve are higher. The pump has no trouble lifting a couple of feet, and that is all it takes. But I don't like the idea of lifting, then dropping down and lifting again. Even though the 2nd lift is considerably lower than the top of the loop -- so it should effectively drain since it was already lifted higher -- I just hate that 2nd climb.
The only way to avoid that is to wait 10 feet before making the lift, as in Option B. Waiting to lift once, only when it gets near the tank, puts the lift 10 feet away from the pump on the back of the toilet that I wonder if that will cause more problems. I might be better off lifting early, even though it needs to go downhill then back up. BTW, it was originally installed with option A. I just wonder if Option B would be an improvement, or a drawback.