Another Black Tank Issue

[drillagent]

When we purchased our used 2012 3750FL, DW and I took it out on a shakedown cruise. There were a couple of issues that were easily fixed, so no further problems there. But when I emptied the black tank, I noticed there was still fluid and some solids still in the bottom of the tank. I flushed the tank several times using the built in tank flusher. Weak flow by the way. Even after I stuck a hose down the toilet. I even filled it with a 5 gallon bucket to verify the capacity. There's always fluid and gunk left over. I can't seem to get everything out. You may find this gross, but I even taped my iPhone to a yard stick, turned on the video camera, and stuck it down the toilet to see what was down there.

So after reviewing the tape, I noticed that the tank empties at the side, right below the toilet. And right in front of the hole, there seems to be a bulge in the tank. Right below the toilet where everything drops. It's about 1/4 inch below the level of the drain pipe. The rest of the tank drains just fine, but there's always this large puddle of nastiness left over.

Just to be clear, my intent is to NOT leave the tank completely dry. I generally pour in a five gallon bucket with RV RidX and Calgon after I flush the tank. But I'd love to be able to get all the nastiness out before I do that.

Is this an inherent problem with all black tanks, or is it just mine? How do I get rid of the bulge/puddle? Is this something I need to take to a dealer to fix, I can fix myself, or am I just up a puddle without a paddle and have to live with it? Thanks in advance for any help.

[1retired06]

On many black tanks, including mine, the toilet does not dump directly into the tank, but rather thru an elbow. If you have a bulge that collects and does not drain, I wonder why you cannot flush the bulge with a hose and blow everything out. Then it would be a matter of a second flushing each time. Have you tried completely refilling the tank, via hose thru the toilet and flushing, or letting a hose run thru the toilet for a while with the valve open? Likely there is 2 plus years of crud layered up and it will take some time to get it all loose and out.

[DonandBonnie]

These tanks are plastic and somewhat flexible. They can sag somewhat with the weight of liquids in them, thus making complete discharge difficult. We realize that everyone has their preferences for tank cleanliness. For us it's like horseshoes and hand grenades - close is good enough. We turn on the black tank flush as we begin to dump. When the discharge flowing through the clear fitting is close to clear we figure we are done. The particles that don't dump this time can dump next time. Dumping weekly regardless of how much is accumulated in the tank, along with regular use of an odor/liquefying chemical keeps any unpleasantness out of the living quarters.

[DQDick]

X2 for us. We dump twice a week when stationary, flush till clear then add Happy Camper and move on to other more fun activities.

[bigskyjimmy]

Yep ,I do the same as DonandBonnie and it has worked out great for me as well 99% of the time