I did try that first but couldn't get it to come out that way. My fitting just wasn't getting in there enough to create the pressure I needed or that clog was just REALLY in there.

I also took the cap off and the gasket was torn up pretty bad. So I went to autozone, got a sheet of gasket maker and cut one to fit. Washed her bike to get all the gunk off and worked like a charm!

 

I had the same problem and it took a full riding season for me to figure out what it was. My issue was that there was a kink in the overflow hose under the gas tank. The kink happened when the previous owner unscrewed and lifted the gas tank.

I only figured it out when I had to lift the gas tank to do some work on my bike. When putting the tank back down, I realized that the hosed was bent and kinked. After straightening it out, the overflow water drained like usual.

For anyone that has a similar issue, slightly pulling on the hose should straighten the kink.