flagstaff hw27sc 2007 used, sink wont drain

[camper carl]

Just bought unit used and sink wont drain without dump valve open. I verified 6.5 gallon tank. Checked vent stack in cabinet near sink bowl and replaced for good measure and still wont drain. If I unscrew the stack vent until it lets air out around the threads, then it drains. What am I missing here?
Thanks

[Bama Rambler]

What you're describing is one of those vacuum breakers under the sink. They allow air in under normal circumstances but not out. You'll have to vent the grey water tank itself for the air to escape and allow water in. I'm not familiar with how that's done on your unit but it has to be done at the tank.

[BigDTx]

are you sure the grey tank is empty you are deraining into? Could the tank be full?

[richardkhunter]

Camper Carl - We're very interested in the exact same model (HW27SC) a 2008... I realize you've only had it a short time, but would love to know how you like it. Did you have a pop-up before, for instance?

Thanks, RKH