Questions about 1983 V20 fuel tank

[bilgsmf]

I bought my 1983 V20 step-lift about 4 years ago. Its been sitting in my covered patio since then. The only thing ive done is to install my Yamaha 150 on it. The boat is in good shape but now that I am ready to start working on it, im wondering what I should do, if anything, about my gas tank. Its probably been sitting a year or so with what ever gas was in it when i bought it. Owner never said there were any problems with the fuel system. So should I be worried about putting new gas in it, or is there someway to flush it out first? Any recommendations would be appreciated. Also, does anybody know the capacity of this tank?