sealing a custom gas tank

i just finished making a custom gas tank for my s10 and it needs sealed before i start using it. i bought some gas tank sealer from the local radiator shop and i need some advice on the best way to get it to coat the entire inside of the tank. the guy i bought it from said one quart was enough to do my tank and that i should slosh it around and let it dry for 1-2 days. does anyone know of a good technique to get the sealer to totally coat the inside of the tank, it seems like sloshing it around wouldnt work well becasue this stuff is more like a super thick syrup than a liquid. its a rectangular shaped tank with baffles inside so getting a nice even coat of sealer is going to be hard. any ideas?