Secondary Gas tank. Dual tanks

[8T3GMC]

Hey you all. I got a new selecter switch for my 83 GMC. I was just wondering if there was a drain on the gas tanks of these trucks. It does have duel tanks. The driver side one has always work. but the passenger side worked once and they said it didn't again and had it disconnected. I want to fix it to have 2 tanks. But if its going to be a whole ordeal and mess then I will forget about it for a few years. But I was wanting to ask a little about them first.So anyone have advice on how to fix it. I have ordered a new selecter switch. just hoping that valve and all is good and that there aint gas from 1983 in it.