Help locating Blazer bed hole(s) for Fuel tank.

[Thealien]

That is factory and part of the gas tank vent and emission system. There are two vents from the gas tank that both go to that tube. Then one line goes all the way to the front to the charcoal cannister which when working properly will burn off gas vapors/fumes while you drive.

Over time many of the vent lines in that system get clogged and can cause problems. Sometimes you can blow or clean out the metal tubes and replace the rubber lines and get it working properly. There are some discussions on taking the charcoal cannisters apart and putting new charcoal inside.

There are 3 ports at the charcoal cannister. One goes to the line from the tank and that tube. 1 line goes to manifold vacuum, and the third line goes to ported vacuum so there is only vacuum to the charcoal cannister off idle I believe?