Since we're not doing anything longer than three or four day trips because of COVID, I'm continuing to knock out those little things "I'd like to do" type projects (not spending money on fuel, so might as well spend it on other stuff).
Our black water tank (70 gal) has a simple 'Tank is full' light - Dometic DTM01 system. Basically a light comes on when the level is about two inches from the top of the tank. Since we'd pull in for fuel every few days when cruising that two inches has never been a problem, and provided plenty of warning. One thing I didn't like about it was not knowing how 'empty' the tank was when we were off shore and I ran the macerator and pumped overboard. I wanted a better feel for the tank level as it was empting. The boat has an analog gauge for the potable water tank - but figured, might as well put in the same system for it too.
Purchased the Dometic DTM08 system and two three inch adapter flanges.
First job was to build a wire harness to go from the tank level probes to the display panel. There’s some minor modification (flipping of probe sensor magnets) that you need to do to differentiate the black water (filling triggers lights) and potable water tank (empting triggers lights). Bench testing everything before getting started was fairly easy.
Next, time to access both of the tanks. They’re located under the rack in the aft cabin of our 4100 SCA - a bit of a pain. Lots of angle bracket screws to take off the top of the bed frame - of which I’m only putting a few back in.
The potable water tank is easily accessed - it’s above the deck in the middle of the rack. The black water tank, on the other hand, is under the deck, at the foot of the rack, under the pull out drawers. So, remove the drawer, remove a ‘false floor’ - basically a ‘base’ of the bed frame, then cut through the carpet & deck to expose the top of the tank.
After cutting holes to accept the adapter flanges, cutting the ‘empty’ and ‘half full’ level rods to length was super easy. Cutting a bulkhead to install the display panel was easy. As with most projects running the wiring was the biggest job involving the usual contortionist maneuvers in the bilge area and use of a fish tape and chase strings. In the end everything went in nicely and works/looks great. Certainly not a ‘needed’ upgrade, but a nice project we enjoyed working on.
Aft cabin rack ‘opened up’ to expose the potable water tank (here with probe already installed). You can see the drawer removed at the foot of the bed to get to the black water tank.
Exposing the top of the black water tank.
Black water tank flange installed - you can see the old DTM01 probe also.
Tank level probe cut to length and ready to go into the black water tank.