One of the more common complaints we hear about RVs these days is holding tank sensor failure. Although not an
earth shattering problem, it is a real irritant, nonetheless, especially for those unlucky enough to have a black
water holding tank that's not located directly under the toilet. Not being able to see directly down into the tank
has definite drawbacks.
The malfunction usually becomes noticeable when waste water starts backing up into the toilet, sink, or shower, but
your gauges show that the tank is only a quarter full. Yuck! Aside from cleaning up the disgusting mess, the
problem is usually relatively easy to diagnose and correct.
The problem is either mechanical, electrical, or the result of a dirty in-tank sending unit. Here's a good,
inexpensive way to find out if a dirty sending unit is indeed the culprit, and most times fix it if it is.
The next time you put your RV up between trips make sure you've emptied and thoroughly rinsed the holding tank.
Then fill it with fresh water to nearly full, add the correct amount of an excellent quality bacteria type liquid
holding tank chemical for the capacity of the tank, and fill it the rest of the way with water.
Let the RV sit as long as you can without adding anything to the tank. This will allow the bacteria and the enzymes
they produce to do their job of digesting any toilet paper or organic debris that may be clinging to the sensors.
Finally, before your next outing, simply empty and thoroughly rinse the tank once again. If you have allowed
sufficient time (a week or so should do it) for the product to work the sensors should read correctly. If they
don't then the problem is either mechanical or electrical and you'll want to ask Les to help you troubleshoot via
the RVers Corner bulletin board. If all else fails you'll have to take the RV to a service center for additional
diagnosis and repair.
We also recommend that this procedure be performed on an annual basis to keep both your grey and black water
holding tanks, sensors, and dump valves pristine clean. At about a dollar to treat a 40 gallon holding tank,
this is the least expensive insurance you'll ever buy.
Remember that extremely dirty holding tanks didn't get that way overnight. Be sure to allow the enzymes enough time
to 'eat' their way through all of the accumulated crud.
Regular use of a high quality liquid enzyme producing bacteria type holding tank chemical, along with proper
holding tank dumping techniques, should prevent any reoccurrence of fouled holding tank sensors.
Okay, now you ask, what IS the 'proper' way to dump your holding tanks?
Here's what we recommend. Empty the holding tanks when near full by first dumping the black water tank and then,
after it's drained and with the black tank valve still open, the grey water. When all the sewage has drained, close
You'll want to rinse out the sewer hose before storing it but, if using a good liquid bacteria holding tank
chemical, will be pleasantly surprised at how clean it is even before it's rinsed. As for rinsing out the tanks
after draining, well, our customers tell us they usually don't have to. Again, if using a quality product, the
contents of the tank will be almost completely liquid and will empty fast and clean.
We also suggest that you add a couple of gallons or so of water and the appropriate amount of chemical to your
empty holding tanks before storing your RV. The chemical will continue cleaning your tanks and you'll be ready to
go without having to worry about that minor chore before your next outing.
If you can gain access to your tanks you can determine their capacity with the following simple formula. All
measurements are in inches.
L x W x H divided by 231 = capacity in gallons.
Example (my fresh water holding tank): 50" x 21" x 16" = 16,800 divided by 231 = 72.72 gal.
capacity (close approximation).
Dirty sensors can give false reading, not only showing fuller than they really are but under
reporting as well.
I bought and use the Flo-Jet Waste Water Pump kit and I LOVE IT! No more waiting at the dump station or paying
fees to dump or finding an open dump station. I simply connect the portable pump, run a small diameter hose to my
homes sewer clean out and press a button. Problem solved. Read more at: http://www.rverscorner.com/Flojet_RV_Waste_Water_Pump_Kit.html
Disclosure: Advertisements are placed on this website to offset the cost of maintenance and to
keep this site free for everyone to use. Owners of this website will receive compensation for products and services
purchased through featured advertisements. All claims of actual user results should be considered atypical.