Better waste tank monitoring with Maretron

Ben Stein

Ben Stein

Publisher of, passionate marine electronics enthusiast, 100-ton USCG master.

29 Responses

  1. I just replaced two of my Maretron TLM’s with the FPM100 and the 0-1.5 Maretron-branded sensors. Thankfully, I already had SAE openings, so it was a matter of dropping them into the water and diesel tanks, connecting the wires, configuring it on N2KAnalyzer, and done!

    Having used the TLMs for a number of years, I can say that the FPM solution is far superior in terms of accuracy, especially when you get near the top/bottom of the tank. The TLMs always stopped reading reliably once you got close to full, and provided wildly erratic readings at inopportune times.

    The fuel tank in particular is far more accurate than any system I have, and I’ve been able to verify it through the last couple months of usage.

    I haven’t found a good cycling gauge yet. My go-to is any of the DSM series from Maretron, but they are far more than $200!

    • Ben Stein Ben Stein says:

      That’s very interesting Steve. When I started this process I thought for sure Maretron would steer me towards TLMs. I was surprised when they pushed towards the FPM100 but I’ve been quite impressed with how well it works.

  2. D says:

    Installed Sensatank 2-3 years ago on waste and 2 fresh. Sensors on outside of tanks. Probably have to be plastic tanks. Works very well. Quite inexpensive. Easy install

  3. Marathon needs to make this game easier. Requiring Windows 10, a PC (not a Mac), a USB converter, a special program, etc. is a non starter for me. Making displays and conversion kits to be able to easily replace old units would also be a requirement. Same wire would be nice. In short, there is a long ways to go!

    • Ben Stein Ben Stein says:

      Maretron allows you to configure the FPM100 from any of their displays or gateways. By using the SAE 5 bolt cut-out they make it easier for direct replacement of most senders. I’d love to see them offer a mounting kit with the 3″ plugs as well but that certainly wasn’t a difficult procedure. Maretron also says the sensor wire can be extended by 50 feet, so I think you’d likely be able to use the same wire, though there are a lot of different senders out there and quite a few different wiring patterns so there’s nothing universal for them to be able to offer. I don’t think I can agree that there is such a long way to go. I think Maretron has done the hard work by offering a reliable, easily installed option.

  4. Joseph Pica says:

    I had TLM on my holding tank reading to the DSM-250 and had many conversations with them about the focus tube/air lock? on the bottom of the transponder which was made of aluminum. Seems the nasty contents in the holding tanks happily corroded the tube quickly resulting in heavy build ups of aluminum oxides which caused erratic readings. I’m glad they have come up with a better solution, however I hope that the sensor is truly corrosion proof against the contents. The caustic nature of that offal can even eat stainless steel unless it a special grade of stainless. Hence why holding tanks are not made of Stainless steel. Best to you and the girls!

    • Ben Stein Ben Stein says:


      That makes it sound like I might need to do an inspection of the sensor at some point in the future when it’s had some time in the tank. Ugh. I’ll don some gloves in a few months and see what I find.


  5. Colin A says:

    I’m a little surprised they recommend the pressure sensor. My experience with another system using pressure sensors were they tended to fail in 2-4 year time span when in Black Tank service. I assume the sensors Maretron spec’s most be a little more rugged.

  6. greg says:

    ben, i really must complain 🙂 – my black tank sender unit has just developed a problem
    with low level sensor (pump will not run unless pumpout button held depressed continuously, normally it would run after a press untill it senses “empty”).

    Im sure my boat is reading your blog and decided to inconveniently exhibit a senser fault at same time as yours! haha
    .. article was VERY pertinent for me .
    keep up the great work

  7. Dan Corcoran Dan Corcoran says:

    Ultrasonic measurement of waste and fuel tanks were a disappointment on my last boat.

    I recall the TLM product did display on my Raymarine instruments over N2K. How about the FPM100?

    • Ben Stein Ben Stein says:

      It sure does. You can see a screenshot towards the bottom of the article. The top right image of the gallery of four is a Raymarine Axiom screenshot.

      • I’ve been troubleshooting an issue with displaying this data on Furuno equipment. It shows up on Ray, Simrad and Garmin, but does not show up on Furuno TZT2 series displays at all. Something about how Maretron is formulating the PGNs is different between the TLM/TLA and the FPM – not sure if it is Maretron or Furuno’s fault yet!

  8. Mike Field says:

    “If anyone knows of a NMEA 2000 gauge that could easily cycle through the available tanks and display their levels for less than $200, I’m probably in for two.”

    What about using the yacht devices NMEA display?

    • Ben Stein Ben Stein says:


      Good suggestion. I’m actually using one currently and while it does a decent job it’s not as flexible as I’d like. It only supports one fresh water tank for example.

      I’d also really like a round, gauge replacement form-factor.

      Ben S.

  9. Evan Bauman says:

    I’ve used a TLM100 with my holding tank for around 5 years and no problems so far. But could be that our tank sees very little solid waste (we are mostly at our dock at night with very convenient and clean bathrooms). I do use an FPM100 for fuel tank level, fuel pressure (post Racor) and engine inlet manifold pressure. Accurate and super easy to setup using a Maretron display.

  10. Anonymous says:

    While gauges look good, setting the Raymarine to show six numeric values provides a lot of visibility into infrequently used values. For example, I put multiple, tanks, battery voltage, water temp, barometer all together in one display, I believe I had set up another page to show depth in big numbers and swapped between that and the tank info, thereby requiring no dedicated displays for tank information.

  11. Brandon says:

    I am looking to do something similar because my Maretron Ultrasonic really struggles with readings on my waste tank (great on my water tank though). So I plan on buying a FPM100 and one of the transducers. Would you recommend going with the cheaper transducers? Was it worth it?

    Also for any of those reading or who is in need of a very good condition Maretrom TLM ultrasonic sensor I would be willing to sell the old one at a much greater discount than list.

  12. David Torre-Carpenter says:

    Thank you for your post on the senders for the holding tank & so many other useful reviews. On the bosses Offshore 64 I added the TLM By cutting in a new hole and kept the tank watch as a backup to keep the shut-off to the heads functioning. I have had to replace the TLM twice and will now be adding the heads to my FPM system that I used to replace my Tank Sentry system due to the service life & cost of their senders. We have 3 fuel & 2 water tanks that the Tank Sentry system monitor & in 6 years I was about to have to replace the senders for a second time so figured I would give these a try for less than the cost of two of the other senders. Great site thank you again

  13. CMack says:

    Is there any risk that these sensors get damaged during a pumpout? I am setting up the FPM to monitor engine boost and came across this article so was thinking why not monitor my black and freshwater tanks as well.

    • David Torre-Carpenter says:

      I’ve had mine installed on my black water tank & all other tanks for a year & have had no issues.

  14. Samantha Bartlett says:

    Simarine Pico as a monitor?

  15. Wolfgang says:

    Hi Ben,
    Maybe there is an update how this sensors are performing after 2 years?

    • Ben Stein Ben Stein says:


      Thanks for checking in on this. The system continues to perform very well, though I had to make one major change. The Maretron provided — really nice and quite expensive — submersible pressure transducers failed at about the six-month mark. They both failed during pump-outs but not at the same time. I replaced them with roughly $35.00 transducers I got on either Amazon or Ali-Express. These have worked for over a year and a half now with no troubles whatsoever. I sent the Maretron units back to them for them to work with the manufacturer on a failure analysis but haven’t heard back.

      But, the TLM100 and the other sensors I’m using for fresh water continue to work flawlessly and I remain very happy with the project overall. Plus, the cheap pressure transducers are cheap enough that even if they only lasted a year or two I would happily replace them and carry on.

      -Ben S.

      • Wolfgang says:

        Thank you Ben,

        I got a good deal for a brand new FPM100 and wanted to know your experience.
        Based on this I will go also for the Amazon pressure transducers.

        Currently an UTV (Philippi, more or less comparable with TLM100) is causing problems, have to be cleaned regularly to operate. However this ultrasonic was already much much better as the original tankwatch sensor.

        For fresh water ultrasonic is working perfectly in my case too.

        Regards, Wolfgang.

  16. Anonymous says:

    I learned the compatibility of a submersible pressure monitor with the FPM100 here in the comments, which took me to the Maretron site.

    For my application, sailboat racing, I wish I had a better measurement of how low the tank is. We are frequently keeping it between 1/16 and 1/4 tank to save weight.

    A question, how well does it measure when your tank is low? Does that sensor essentially roll around a bit in the tank or do you stabilize it?

  17. Christopher says:

    I was taking measurements at 1 cm 0.1V running from a 1 cm fluid level.
    I use such strainers against neglect
    The sensor is installed permanently in tanks so that it does not move by heavy sea

  18. Anonymous says:

    Permanent, as in glue? Does the tank need to be drained to install it?

  19. Christopher says:

    I have photos of how I mount it without glue 😉 I can send it by e-mail.

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