Heights and Vents
While my experiences may seem less relevant because my model is different in some ways. perhaps some comparisons might still be helpful.
When we bought our boat we were surprised to find that the factory stock method of filling both fresh water tanks was thru a 2 inch screw-out plug in the top of each one. Not like any boat I had owned or crewed on. Our main tank was under the starb. settee and the optional factory tank was under the cockpit seat hatch, way down against the bottom.
Each tank did, OTOH, have the standard EY vent fitting, with the settee tank vented thru a spout on the galley countertop in from of the sink, and the aft head having its separate spout overlooking the head sink.
Since we never would have a problem with an overflowing vent, like all of the boats with a deck fill, this seemed like overkill to me.
(With a deck fill, just about everyone (sooner or later) leaves the water run with the nozzle stuck into the fill opening and only checks on it again when: 1) the water starts shooting back out around the hose and/or 2) the inside vent starts shooting water into the sink.
Since we *always* know when the tank is filled because one of us is holding the hose just inside the top of the tank, we never had water enter into the vent hose. The vent is just there to let air in as we use up the water.
As part of the project to replace the settee tank with a larger one, I replumbed the vent hose up and under the galley counter with a little U fitting at the top. Since this puts it a couple of feet above the tank it should never have water in it unless the boat inverts... and at that point we will other worries.
When I had a new aft tank fabricated that fit the area a *lot* better, I ran a short piece of 1.5" fill hose up by the inside of the cockpit seat and put a fitting with screw-on cap on it. I also ran a vent hose right up beside it. I can see when the tank is about full and just shut off the hose.
Note that we have a little ball valve on the end of the hose -- often found in garden supply stores -- and we can then fill tanks or switch to a nozzle for wash down without going ashore to the head walk to turn the hose off and on.
So.... I wonder if the tank vents on the EY models could be rerouted so that there are no low places in the hose run(s)?
And also kept separate so that no water can wander between tanks?
.....Seems like a concept worth pondering....
Added material: in case anyone was wondering, we kept the fill scheme and do regularly fill the settee tank thru one of the 6" screw-out ports on top (on either side of the internal baffle). This works very very well.