To be USCG (US Coast Guard) compliant, I had to either fit a holding tank or sling the heads before entering US waters. Some Sadler 34 owners have fitted custom holding tanks behind the toilet, in the heads compartment. To get the job done simply, and more economically, I opted for this unattractive approach:
The holding tank is from Tek Tanks of Alton, Hants in England. They have a database of custom tanks for a load of boats, based on previous projects, but I will stick with the current setup for a year or so.
The plan is to hide it behind a wooden shell, made to look like a cabinet. This bulkhead is the driest part of the boat, so I will add a storage space to the right of the tank, (looking at it), for charts, manuals, documents etc. The loss of space would be a pain if there were four or five crew, but it is fine for one or two.
As an aside, my log was completely ruined after crossing Biscay in November 2014. It was “safely” stored in the desk, and water poured in through the leaky port above the desk, as well (I think) as through the open hatchway when a few massive waves snuck up behind me and took out the sprayhood. I then discovered plastic paper log books, which work great with pencil, and are resilient against sea, rain and flood.
I have ordered a Non-contact tank level sensor, from New Providence Marine. It means that I don’t have to fit a mechanical device inside the tank. It comes with a gauge which I will install in the heads compartment, warning people not to flush the loo if the tank is full.
The sensor has two foil strips running vertically, 3″ or 4″ apart, down the outside of the tank. I think it will have to be fitted to the rear of the tank, against the bulkhead.
[When I first bought her, I could not find the holding tank (it was a crappy hand-over). I called or texted from the Irish Sea and learned that there was none. This explained why it was backed up.]
The tank takes up valuable foot space when sleeping in that bunk, unfortunately, but it will be fine for someone 5’8″ or less. And, of course, a place at the dining table is sacrificed, but for the next year or so, it will do. Especially if it is disguised as a cabinet or cupboard!