Im looking for repair manual for 1986 chevy k10 pickup. or at least a diagram of where all the gas lines go

Autozone.com has a lot of info on your truck. Just sign up for free account, enter your truck year, model, etc. and look here: http://www.autozone.com/autozone/repairinfo/repairguide/repairGuideMain.jsp .

To answer the question on fuel tank lines, there should be 3. The pressure line goes to the fuel pump, and a return line from the fuel pump. The third line is the evaporation system/vent line. It goes to the evaporation cannister to control gas emissions. Not sure where that is on your truck. The manual doesn't say.

If you have more questions, please let me know.