On my H356 the run from the toilet to the holding tank had a dip in it as it ran aft in under the aft bunk. I calculated from the hose diameter and length that it would take a gallon of flushing to clear the hose - and that's based on the optimistic assumption that the hose is cleared without any mixing of the flush with the hose contents. So from a forward head, to the aft holding tank that most the Hunters have, I would think it would take 2 -3 gallons to clear the hose. Not to mention that the hose probably runs in the bilge, and each end is higher than the middle. Once you get that hose clear I would make sure you are putting a lot of clean water flush thru that hose whenever you leave the boat or go #2. The best thing I think you can do for head odor is keep flushing. With a clear vent the flushing replaces swamp gas with oxygen. It is the weekdays, for the way many of us use our boats, that cause the odor problems. I also get pump outs ASAP. We're lucky here we have a pump out boat. So on Sunday afternoon I often get the pump out, even if the holding tank is only lightly used. I get pump out as often as I can.