We did a nice sail on Saturday, our first proper sail with the boat. It went pretty well and when we got back, we noticed a lot of water in the forward head and the toilet was full to the brim with sea water. We know it's sea water because the holding tank is empty given the leaking issues I mentioned earlier.
It appears the our boat has no anti-siphon valves on either toilet. So, when its heeled over, water is basically sucked inside the boat from the sea water flush inlet (the electric toilets use sea water for flushes) and into the toilet which overflows in to the boat. Boats have actually sunk this way and the manual for our toilets insists on requiring an anti-siphon valve be installed which Jeanneau seems to be ignoring.
There is a sea cock to close the inlet which we'll need to do but it blows my mind that Jeanneau doesn't fit these standard on their expensive sail boats which are ocean rated. I've asked the dealer if this was a mistake during fitting or if Jeanneau really ships the boats with no anti-siphon valve. This basically means if you want to use the head at sea then you need to open/close the valve or use fresh water from the shower to flush the toilet. We have a head on port and starboard so we could use the high toilet to avoid any water coming in during use.