Sundance 3300sk problem dumping

nugget

Member
When I go to dump my black or grey tank, pull the valve, the liquid rushes out and forms an air lock. I have a clear hose attachment and can see huge air bubles travelling up the line into the tank. Kind of like when a gallon jug full of water is held upside down to drain.
If I open the valve halfway to reduce the flow rate it drains OK as the liquid flows along the bottom of the pipe and air can enter along the top of the pipe.

What causes this?? Are there tank vent pipes? Could they be blocked? Is the slope of the sewer pipe too steep?

Any ideas?? Suggestions??
 

westxsrt10

Perfict Senior Member
You are on the right path regarding the vent lines. Sometimes the installer dosnt slope them up the entire way or traps it, running the vent level or downhill can cause your problem. Block your toliet valve open next time and see if that helps.
 
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