Thanks for being polite... I'll be more straightforward, my first answer was just plain wrong... if I had read your post all the way to the end instead of jumping to a conclusion I (might) not have been so wrong! But I think my theme was in the right direction...
On the aft head intake there is nothing else connected to the thru-hull hose, so a check valve isolating another water user isn't the issue. The hose still gets air in there when you are sailing. We have manual heads on our boat, and I notice the extra pumping to clear air when we are sailing. Since this is a new experience for you, and you know your boat, I'll suggest that the pump is worn and having trouble priming itself when it starts with air.
I don't have enough experience with those electric toilet pumps to give you an idea what might be wrong. Hopefully somebody else here can...
---In amelyachtowners@..., <karkauai@...> wrote :
Hi Bill. I don't think that's the issue. I've had the boat 9 years and it's only been doing this the last month. Also, as I said in my first post, there is a separate thru-hull for the intake just inboard of the head...no sea chest.
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