Black Tank Won’t Drain


It’s gotten cold here in St Louis, however, the temperature has warmed up enough to thaw the drain pipes. Originally, the black tank valve was frozen, and would not budge. Since it’s warmed up constantly for a few day’s, the valve opens freely. However, it’s not draining. I have tank heaters, and poured everywhere antifreeze in the tank. Honestly, I’m not sure whilst gently pulling the valve whilst frozen, if it did open slightly. I’m not sure if the tank slowly drained. The tank level lights are not accurate. Any suggestions??


Well-known member
The tank level readings are almost never accurate after the 1st day of use. It's not unusual for the black tank valve to get a little paper or crud jammed in where the blade seats, allowing a slow leak that empties water out of the tank. If you can flush without the toilet "burping", the tank isn't full.

If you get a clear adapter on the sewer outlet, you'll be able to see whether, with the valve open, water comes out after flushing. For years, I've used a clear adapter with backflush fitting combined with twist-on gate valves before and after the clear adapter. The first gate valve is closed for travel and opened after hooking up the sewer hose. The 2nd gate valve, after, the clear adapter, is closed to backflush the tank to remove blockages. There are also combination devices.


if you think the contents of the tank are frozen try using a warm water salt solution to thaw the tank.


Well-known member
Perhaps pulling on the frozen valve the wire has pulled out of the valve and is not opening the valve. You may have to physically look at the valve to check.


We had an issue of our black tank not draining on our cyclone 4006. The culprit? The black disc that they drilled/punched out when attaching the pipes to the tank was left behind. They did not retrieve it and throw it away like they should have. My husband had to stick his arm up the drain exit to clear the blockage. Heartland literally told us “we got lucky” To discover that so soon and not months down the road. Hopefully that is not what is going on here, but wanted to share our experience just in case it’s useful for you or someone else.