Well well well, we do live and learn.
In any event my thanks for your response. I am on a steep learning
Wishing to replace a tiny 10 litre holding tank.......gravity used to empty, I engaged a company to install a 30 litre one. This, under the settee. Not a best job as the 'plumber' left a sag in the main hose being presumably too lazy to shorten his "near-enough" over long ones. I shortened it.
So the original vent which was about 10" vertically out of the small tank, has been replaced by one exhausting in the same place, but now descending further down, to the top of the new tank sited at floor level beside the centre walk way. So it would be about 5 feet in length running across the new tank, through the outer cubby hole thru' the bulkhead and straight up behind the head
and exiting just below the toe rail.
I think I have solved
the sulphur dioxide (?) smell by paying attention to flushing
properly after use and at the day's end putting fresh water
through the head
(with a Milton tablet) and after dry pumping that, leaving a kettle full of fresh water in the bowl until next time out on the briny.
The idea is that if that don't work I consider passing air into the top of the holding tank with, say an acquarium aerator. I would be assuming that the small tank religiously dumped at sea each day, then thusly treated at the Marina, should be enough.
But it does no harm to think ahead.
I enjoyed your earlier comments in the forum.
I'm glad you're upright and breathing, and available for a stimulating read.