Linux, how long have you had this valve installed? I had it installed for two years, I started experiencing minor filling issues I would have to guess some where after a few months, which progressively got worse to the point where I could only put a few cents in at a time. I was driving the car pretty much daily over this period.
While trying to solve the issue, I found the vac hose connected from the larger barb to the purge solenoid had collasped (I was using Vibrant silicone hose). It looked as if it had been slowly sucked together. It was pretty obvious that vacuum was trying to get through, and that the check valve was preventing it. My guess is that this tiny amount of vacuum had built up over time, eventually leaving pressure in the tank (this is my guess as to what occured). Regardless, once I removed the check valve to test my theory, my filling issues were immediately resolved. So something seems odd here, and maybe I'm not 100% correct, but it does seem as if there should be a multi-port check valve on this vac line, and not a one-way. I also found it odd that there were others complaining of the filling issue in this thread.