Any clever ideas on how to monitor the level in waste holding tank?

Aug 7, 2023
225
catalina catalina 320 norwalk
It's always in the back of my mind; I'd be more comfortable knowing.
 
May 17, 2004
5,079
Beneteau Oceanis 37 Havre de Grace
Assuming it’s a non-metallic tank SCAD is a popular choice. Mads on the Sail Life channel just did a install of one -
 
Jul 1, 2010
962
Catalina 350 Lake Huron
Mine has a monitor strip on it that's pretty useless. A tap with a calibrated knuckle is more accurate. I also installed one of these at about the 80% mark for a backup. Works great and lets me know I've got about a day left when it switches on:

 
Dec 2, 1997
8,729
- - LIttle Rock
I have the SCAD system. I had to install their probe because I have a metal tank.
What makes their internal sensor so much better than any of the usual ones is that the actual SCAD sensor is enclosed in a PVC tube that that prevents waste from having any contact with it, same as sensors that attach to the outside of any tank that isn't metal.

Keep a close eye on that tank for leaks, Justin...urine is so corrosive that it turns any metal holding tank, even 316 stainless, into a colander in an average of about 10 years...and it's not unusual for a leak at a seam or fitting to show up in about 5 years.

--Peggie
 
Last edited:
Dec 2, 1997
8,729
- - LIttle Rock
You aren't likely to see anything but actual leaks checking the outside of the tank..the damage is happening on the inside. If there's an inspection port in the tank (if there isn't I strongly recommend you install one), you be smart to use it to check the inside of the tank a at least a couple of times a year/season to check the progress of the pitting in the tank bottom and the lowest part of the vertical walls. That'll require thoroughly rinsing out the tank first, which isn't hard to do: just pump out and then put about 6" of water into the tank via deck pumpout fitting 'cuz that sends the water into the tank at the bottom to stir up any sludge so it can be pumped out. Pump that out and repeat till you're pumping out only clean water. Now you can see the bottom of the tank.

You may already be doing this...if so, great. I always try to keep in mind that forum posts aren't private conversations....that every site has zillions of lurkers in addition to all the posters so I try to post advice for anyone who might read it and find it useful.

--Peggie
 

4arch

.
Jun 29, 2010
101
Beneteau Oceanis 400 Baltimore
I bought one of the cheap liquid sensors from Amazon shown in this video and hooked it up to a 9v battery. I used it to calibrate and occasionally recheck the calibration on an existing SCAD system. It's a handy little device to have around, and would be better than nothing if I had absolutely no monitoring device. People have even chained them together to create a full-fledged tank monitor on a budget. They don't work on metal tanks.
 
Jan 19, 2010
1,171
Catalina 34 Casco Bay
I bought a 3 tank external monitoring system from an RV website. Each tank has a HIGH, MEDIUM and LOW. These are self sticking tabs and come plenty of wire on each harness. The monitor panel shows BLACK, GRAY and FRESH water.
 
Jul 7, 2004
8,402
Hunter 30T Cheney, KS
I don't see any no contact fluid sensors on Amazon?
Amazon isn't always the best or cheapest place to shop. Defender has good prices.
 
Jan 19, 2010
1,171
Catalina 34 Casco Bay
if it works well can you give me the brand name please.
RecPro is the system that I installed..

There are multiple offerings out there. Search: External 3 tank monitoring system for RVs. or wordage along those lines..
 
  • Like
Likes: jssailem
Aug 7, 2023
225
catalina catalina 320 norwalk
for $11 I bought it. I tried it on a number of jars in my refrigerator and could not get it to work consistently . I had a jar of olives in water that I thought was closest to a holding tank. Worked fine in the beginning and then tried it later on and it did not work. it did work on four or five different things though. but I could never get the signal light to work. I tried every possible combination of wires but never got it to come on. The best I did it was bright and brighter but never off and on. Oh well
 

4arch

.
Jun 29, 2010
101
Beneteau Oceanis 400 Baltimore
for $11 I bought it. I tried it on a number of jars in my refrigerator and could not get it to work consistently . I had a jar of olives in water that I thought was closest to a holding tank. Worked fine in the beginning and then tried it later on and it did not work. it did work on four or five different things though. but I could never get the signal light to work. I tried every possible combination of wires but never got it to come on. The best I did it was bright and brighter but never off and on. Oh well
Hmm that's too bad. Mine has worked pretty reliably and the light goes on and off. Maybe you got a dud?
 
Aug 7, 2023
225
catalina catalina 320 norwalk
Hmm that's too bad. Mine has worked pretty reliably and the light goes on and off. Maybe you got a dud?
The LED light on the sensor itself works fine but I need a remote light so I can see when the tank is full and I can't make that light work. Do you know how to connect a remote light? what wires do I connect. The schematic they give you does not seem to help.
 

4arch

.
Jun 29, 2010
101
Beneteau Oceanis 400 Baltimore
Yellow wire goes to negative side of external LED, positive side of LED goes to power source, brown wire goes to power source, black and blue wires go to negative ground.