Yes there is a level at which the generator pickup starts sucking air. That's to keep you from stranding yourself when the generator sucks the fuel tank dry.
If you're brave try sucking instead of blowing on the line. Start with a really slow light suck. You will know right away, either you are sucking liquid or you are sucking air. Just be ready to get your mouth out of the way.
Or go fill up the tank and see if you get better results.
Yes my mind goes there too, but keep it clean.
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2001 Suburban 4x4. 6.0L, 4.10 3/4 ton **** 2005 Jayco Jay Flight 27BH **** 1986 Coleman Columbia Popup