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Old 10-12-2010, 06:28 PM   #1
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Location: Sequim, WA
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Replacing Black Tank Sensors

Like many others, we have experienced flaky black tank sensor readings. The other readings have been reliable so replacement of the whole system was not considered.

Being both lazy and cheap gives rise to internal conflict when trying to make decisions of this kind. New, sophisticated, fancy monitoring system? Installed by a commercial shop? Not cheap.

Buy new sensors and install them myself? Not attractive to the lazy side.

But, oil change looms, generator is due for service, and steer tires need replacing. So in the end, cheap trumped lazy.

I've no financial interest in Horst Miracle Probes. They just appealed to me as a good balance between cost, ease of installation, and likelihood of acceptable performance.

Horst Mircacle Probes - Click here to go to Horst web site.

The 2001 Diplomat wet bay was not designed and constructed with an eye toward replacing black or grey tank sensors. Fortunately the gray tank sensors are working well and only the black tank sensors needed replacing.

The original sensors are of a type that is glued in and are not removable, so holes needed to be drilled near the old sensor locations to accept the new probes. That way the new probes can use the existing wires and report tank levels as the original design intended. Gaining access to the holding tank by removing the large PVC wet bay panel is very difficult in terms of disconnecting plumbing and other fittings. So I elected to cut holes in the panel with a hole saw to access the old sensors and install the new ones. Now, if they ever need to be cleaned or replaced the holes are already there.

To avoid drilling into the tank, a piece of 7/16" OSB (oriented strand board) was placed behind the panel. The panel can be pulled away from the holding tanks some amount if the mounting screws and brackets are first removed.

The pilot drill length was adjusted to prevent its penetration into the tank. Extraneous holes in the black tank would surely be a source of great unpleasantness.

The positions of the holes were established with a ruler and measuring tape. I started with 1" holes but they were too small to work through. The second two were cut with a 1.5" hole saw.

Once the holes were cut it was relatively easy to unscrew the nut that fastened the wire to the existing sensor, drill a 3/8" hole in the black tank, and insert the Miracle Probe. Some fiddling was needed to orient the new probe so that the seal was tight and the milled flat on the threaded stud was facing down. This is required to keep the Teflon shield (roof, tunnel, etc.) positioned over the probe which serves to prevent hair, toilet paper, and other matter from hanging up on the probe itself. Once the probe assembly was secure in its hole it was easy to attach the wire which already had a crimped on eyelet.

Covers for the holes were fashioned out of PVC pipe caps. I'm lucky enough to have a lathe which came in handy for this. However, I would have been happy to use bottle caps or any other handy material, securing them with a little caulking.

We just returned from a 2.5 week trip to Arizona and the probes worked perfectly. If for some reason they fail to perform as advertised and require cleaning or repair or replacement, the hard part has already been done. I can simply remove the cover in the hole and proceed with whatever action is required.


Dave & Cathy, 2002 Country Coach Affinity, 42', #6103, CAT C12, 2018 GMC Acadia
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Old 10-12-2010, 06:39 PM   #2
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Great work and just an outstanding write up Dave! With so many of us fighting this problem I'm sure many will benefit from you taking the time to share in such a professional manner. If only our manuals were easy to understand!



Rick, Nancy, Peanut & Lola our Westie Dogs & Bailey the Sheltie.

2007 Itasca Ellipse 40FD
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Old 10-13-2010, 06:31 AM   #3
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Great write up & pics Dave. I will be replacing my black water tank probes also.
Del & Lori 2007 Diplomat 40PDQ - 2009 Jeep Wrangler Unlimited Rubicon. M&G brake system
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Old 10-13-2010, 07:21 PM   #4
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I replaced my gray and black tank probes last January with Horst Miracle Probes. They are working great. My comments & pics are on my website here ...the price was much more reasonable than other options, and they were pretty easy to install after I got access to the tanks.
Paul (KE5LXU) ...was fulltimin', now parttimin'
'03 Winnebago UA 40e / '05 Honda Odyssey toad
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Old 06-10-2017, 12:12 PM   #5
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Great write up. I'll be referring to this later down my list of "Must do's".
Tom & Ann Stillman
Vancouver, WA - 360-600-5349
2006 Monaco Knight 38ft PDQ
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Old 06-10-2017, 01:10 PM   #6
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Thanks Dave! Excellent documentation!

Joe & Annette

2002 Monaco Windsor 40PBT, 2013 Honda CRV AWD
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