Boat Waste Tank Gauge

Does anyone know of a quality and accurate gauge for a boat 75 gal. waste tank? Lots of water measuring gauges but few that spell out measuring waste.
I would really feel better with a personal recommendation. Thanks much.

 

Google " rv holding tank sensors "

 

Yes, this is not a job where re-purposing a fuel sender will work.

The common off the shelf solution involves a sealed tube with magnetic reed switches inside, a doughnut shaped float goes over the tube (with a flange at the bottom to stop it falling off).

The float has magnets and will switch the low medium and full switches as it rises.

The downside is you can't use just any standard gauge and is not as accurate, but it is sealed.

Some tank materials will allow a series of ultrasonic sensors to be glued to the outside that go from open to closed as liquid becomes present at the other side.

 

Totally random thought: there is air in the tank, right? Because of the vent this air may not be the same temperature as the fresh poop or pee. In fact a fresh one will be warm.

In another thread hereabouts people were discussing the use of IR technology to look inside structures. How about using a system that is keyed to the use of the toilet. This would permit two strategies. First the sensor could locate the level the more recent addition settles at and second whatever temperature difference there may be between the air and the ... stuff ... may show up. Between them the sensor could keep track of the level and intermittent use would help to keep electricity use down.

Could be salable to early adopters who who want to keep up with the latest ... stuff.

 

My personal solution is a sight glass. Nearly infallible: It does get plugged with poop at the bottom, so I have a routine of periodically taking the dinghy inflation pump and pumping air down the sight glass from above to blow it clear.

 

Even the number one portable toilet maker Thetford doesn't offer more than a simple float switch and a red LED warning light telling the user the tank is full to the brim.

RVs and caravans employ a simple current measuring circuit in the "gray water" tank, with 4 stainless screws in the tank's wall and a 4 stage display. It works only when the tank is new or recently cleaned.

If you really want an accurate indication, use a vertical plastic tube, protruding above the top of the tank and connected to a pressure transducer or a mechanical pressure gauge. The pressure of the air column in the tube indicates the fluid level.

 

All the gauges that use electric die in the tank.

This is a remote reading unit that can measure ALL your tanks , waste , water , fuel , what ever you need.

Should it plug up all that is required is a bit of air pressure to clear it.

tanktender.com/
An introduction and summary of the benefits of a Tank Tender by Hart Systems.
Hart Systems - About Tank Tender
tanktender.com/about.html
An introduction and summary of the benefits of a Tank Tender by Hart Systems.

 

Tank tender is interesting.
Gobius makes a system with no need to make holes to the tank: http://www.gobius.se/fmmarin/

Ultrasonic level measurement is another option: http://www.philippi-online.de/index.php5?url=produkte.php5&m1id=2&sprache=en&kat1_nr=3&kat2_nr=5

With plastic tanks also a capacitive sensor through the tank wall could be used, but I haven't seen any on the market. I'm planing to make one for my boat.

 

A common industrial solution, where there is a requirement for nothing inside the tanks, is weight.

75 gallons will weigh about 625 pounds

The tank does need it's own structural integrity as it supported on four points (corners).

Using a couple of blocks at one side and a pair of e.g 200 pound load cells at the other would give a very accurate weight allowing the used capacity to be shown.

These are getting quite cheap and a pair of load cells plus the electronics can be had for under 100 bucks

 

Fitted over a hundred SEALAND TANK WATCH never been any problems.

 

In terms of water efficiency nothing beats an RV toilet .

Of course it must be mounted directly on top of the holding tank.

NA hate that restriction as much as they hate servicable fuel tanks , instead of boxes for fuel

If its a new build use the RV system , no gauge required , you simply look in from above.