Issue emptying black tank

Freeriver · 06-28-2021, 07:45 AM

We have our fifth wheel at a resort and have a tiny cabin and generally use the restroom in the cabin. Had the grandkids up this week and they all stayed in the fifth wheel so the restroom in the camper got used a good bit. When I went to empty the tanks, very little came out of the black tank though it registered 1/3 full. I added water to the tank to get it to 2/3 full thinking something must be obstructing and hoping an increase in volume would push it through. Nothing came out. Fortunately we also have a macerator pump. First time ever to use, but it emptied the tank. Anyone have an idea what the issue is with the main valve? I also noticed the gray tank (one of them) still showed 1/3 full even though water had stopped coming out when I emptied. I figured the sensor must be bad.

**JFlightRisk** · 06-28-2021, 08:43 AM

The OEM sensors are prone to getting "stuff" on them, and reading false. The probe is basically a smooth screw head in a rubber grommet, and it's very close to the tank sidewall. TP or soap suds on them will give you a reading on the monitor. I had a similar issue with our gray tank, and replaced the originals with Horst Miracle Probes.

EvilDoer · 06-28-2021, 08:45 AM

Hard to say it's a valve issue. I cringed at the word "grandkids". Don't know how experienced they are with rv plumbing, but generally speaking kids are the problem. Adding water, trying to dump, and connecting the macerator probably soaked and softened everything enough to empty the tank.
I'd fill the tanks again (with water), let them soak a bit, and see how they drain.

**JFlightRisk** · 06-28-2021, 08:51 AM

Another thought. Wait about an hour or two after draining the tank before you check the monitor. Sometimes it'll read empty after it's sat empty for a bit.

Jagiven · 06-28-2021, 09:32 AM

The sensors are notoriously inaccurate.

In regards to the black tank, I suspect there was not enough water in the tank when you went to dump it. I would rapidly dump a couple 5 gallon buckets of water down the toilet to help break up any poop pyramid that is building up. Hopefully it has not dried.

After emptying the tank, make a habit to put at least 5-10 gallons of clear water back into the thank. A dry tank will cause you a lot of future issues.

RayPayne · 07-01-2021, 08:52 AM

My black tank sensors in the lower half of the tank never read as empty. I tried the Unique treatment for the black tank and after a couple of uses my sensors actually work again. Perhaps it could help if your grey tank sensors are misreading as well.

This is the video where I learned about it. (National RV training tech tips channel on YouTube)

https://youtu.be/GyWMyZ02_7M

You may also like: