Draining the black water

[Bill_C]

We have had numerous trailers with black water tanks. With our new Rockwood 5er when I open the black water to empty the tank it seems the hose fills up then stops draining as if there is an air lock. I manually lift the hose and work the liquid to the sewer connection, get a gulping sound of air and the hose empties. I go back to the trailer connection and do this all again till the hose is empty. The vent pipe is definitly open to the black tank. I will mention here that this is the first trailer that I have been using the threaded connection to the sewer, which seems to be mandatory in most camp grounds now. (good idea)! With the vent pipe you would not think there could be an air lock. Any ideas ??

[windrider]

Have to ask, how do you know the vent pipe is open?

To verify, I would pull the cap off, and put a water hose in the vent, and turn it on, then watch the monitor panel.

Also, next time you dump the black tank. once it fills the the sewer hose, go flush and hold open the toilet and see what happens.

Sure sounds like a blocked vent pipe.

[Bill_C]

Just the fact I was on the roof once and could smell the fumes. I will try the water down the vent as I also lean toward a blocked vent. Hoping for an easy victory over this one. Alas, why should this problem be any different?

[jimh]

i've had that happen, always just thought there were a lot of solids in there. mine would only do that every so often. once i got it flowing, it would go without farther assistance.

[herk7769]

Either of these answers could be your problem, but my money is on Jim's answer.

I would also be hesitant to put a hose down the vent pipe and run water unless you are sure it is empty. You could use a stiff hose to "push" whatever is blocking the vent down into the tank. (maybe a dead squirrel if the cap is gone or a bee nest)

Reasoning for the tank clog:
If the floor of your black tank has a layer of solids that partially blocks the drain valve, fresh solids could plug the valve easily. When you "burp" the hose, you could be pushing the fresh solids up into the tank allowing a "rush" of water to push those solids through the hole.

You sound like a candidate for a RV-Digest-It treatment or two. Use the "clogged tank" instructions on the bottle. RV-Digest-It.com - RV-Digest-It


If the treatment does not solve your problem, a blockage

[Bill_C]

I had a chance to get onto the trailer roof today and I filled the black water tank through the vent, so it is clear (had the water right up to the toilet, never been that full before). When I drained it, it blurped like usual, air locked, then let go. There must have been something inside the tank that was blocking the drain and with a full tank of water pushed it through. No idea what it could have been as the unit is only 4 months old. Thanks for the help and ideas.