RV Black tank dumping problems and sensors not reading correct are among the most discussed topics on RV forums. Most RV'ers have or will experience the dreaded black tank will not drain; and or the sensor reading of black tank does not reflect reality. Owners of macerating toilets such as the Thetford Tecma toilet have seen the dreaded Red Light
on their wall mounted controller, when they know their tank is empty.
After several years of living with the problem, I was resolute to improve my black tank draining and get better sensor readout. In my 2007 Newmar MADP 4528 chemicals, and my built-in tank quick flusher have been only partially successful. The front mounted Newmar tank monitor system has non-contact sensors mounted on the outside walls of tanks. Link: https://tankedge.com/accessories.html
The rear Thetford Tecma toilet in the Mountain Aire has had many episodes of the dreaded red light and will not normally flush, with an empty tank, without an override. The DW has not been happy with this and I do hear about it. Removed the peg board in front of the drive wheels, passenger side, and located the two rear toilet tank sensors.
They were secure and correctly mounted. All the wiring looked good. Thought about it awhile and the DW suggested to relocate the sensors, to see if that would get a different result.
Cleaned the new tank location with denatured alcohol, peeled the old double-sided sticky tape from sensors, moved the wiring and remounted the two sensors using 3-M brand outside rated, 10 lb double sided sticky tape. DW went inside to check the rear toilet and No Red Light! Eureka, the real culprit here was the build-up on the inside of the black tank wall effecting the rear toilet sensors and also the primary tank level sensors readout. The only real confusion was why did the Newmar installed internal tank flusher not help, even with frequent usage?
Located Newmar's built-in tank flusher, driver's side wet bay, behind the usual plumbing white panel. This is the opposite side of the coach from all the tank sensors on the passenger side. Why did Newmar mount it there? Looked up the tank flusher manufacture' s installation recommendations and the second line of the instructions said to locate opposite end from drain. Only reason to mount it on the drain end of the tank, I can think of, is that was just easy. Definition of Easy is " not difficult, not causing problems or difficulty, or not requiring much effort, work, or thought. Bad Newmar!
Knew I had to get a tank flusher near the sensor, passenger side, to attempt remove the black tank wall crud.
See drawing, look at the two reduced height black tank sections for frame members. This is an another design flaw, in my opinion, that totally rendered the built in tank flusher useless for most of the tank volume. There is no way the tank flusher can get through the two dropped sections at frame members to the opposite end of tank, where the sensor is. Again, Bad Newmar. I hope they have improved their 2007 design on later models, but I suspect they and many other Class A manufacture's use the same tank design. It would behoove RV owners to look at their black tank design. Enough gloom and doom, on to the Fix!
Removed the wet bay white plumbing panel, located the flush tank PEX piping, followed it from hose connection to vacuum breaker (anti-siphon device) in mid-coach bathroom cabinet and back to the built-in tank flusher. Cut the PEX pipe about 2-foot short of the flusher and ran new 1/2"PEX tubing to a new three ball valve manifold mounted on back side of existing white plumbing panel. Mounted the three ball valves with aluminum strap, secured from front of panel with self tapping screws, just like the water tank fill valve. Had new plastic labels engraved at local trophy shop, applied contact cement and carefully placed new Labels for valves.
Ran new 1/2" PEX tubing to existing drain side tank flusher and two new long runs above tanks to passenger side peg board area. The three new ball valves allow me to select which end of black to flush and to also flush the passenger side of the gray tank. I added the new gray tank flusher, so the grey tank sensors and tank could also get a rinsing.
Selected the Camco Tornado flusher for the two new flushing locations.
The rotating head with 10 jets appears to get better results than the fixed spray nozzle one that Newmar installed. I do have a word of caution here, check for proper rotation prior to installing in tank. I checked both with direct hose hoop-up with the DW holding the end of the hose. One did not rotate, one was great. Returned the defective one and the replacement worked great also. For some reason the DW would not again hold the replacement Tornado, at end of garden hose to check rotation, LOL.
First Test of New Flushing system: Hooked up the dedicated flushing hose to white plumbing panel connection, turned on water. Closed gray blade valve and pulled the black tank blade valve to do a dump. Once dump was done I turned on ball valve controlling the Tornado Black tank flusher at the sensor end of black tank. Observed the clear section in sewer hose. The results were things flowing, flowing, and flowing through that clear section for about 10 minutes. Then I closed that valve and opened the fixed nozzle flusher at the drain end of the black tank. Got some more out for a couple of minutes. Then repeated the process at the other end of the tank till it again ran clear, then drain end again. I had never extracted that much debris from the Black tank. The gray tank also had much more debris in it than I thought possible.
Have done four more complete flushes since I installed the New flushing system and front main tank sensor readout has been spot on as to tank levels. Thetford Tecma toilet wall mounted controller is green when tank is empty, goes to yellow with the tank 1/2 full. The yellow Tecma light agrees with the front tank monitoring system, 1/2 full black tank. The Black tank drains much quicker now and just sounds like a more effective drain process.
Highly recommend you install additional built-in tank flushers in your Black and Gray tanks, to correct sensor readings and insure that your black tank dumps quickly every time. Rear bath units with Thetford Tecma toilet will also benefit. Many dollars, IMHO, have been spent chasing perfectly good Tecma sensors and controls.
Best $245 dollars I have ever spent on my RV.