Question for blazer poly tank users

[truckhp]

Dumb question but here goes... what is the configuration of the fuel tank connections, I have two near the filler inlet and one by the sender, not sure whats a vent or return (what I can cap and what I cant) I purchased the tank years ago from Classic Heartbeat but cant get any info on the configuration. Go easy on me guys

[GMCPaul]

Usa them all for vents, tie one into the fuel filler tube near the top and use a vented gas cap, then run a rubber line from the other 2 and attach above high point on tank to vent tank while fueling, plug any of them and you slow the rate that you can fill the tank at, all of them venting air and it will take 3-4 minutes to fill the tank with all plugged 15-20 minutes or more to fill the tank as you are then preventing the tank from expelling air as it fills and with all plugged gas will back up in the filler neck as you fill and burp out the filler tube as you try to fill it.
GMCPaul