So after just one night of evaporust the tank is in amazing shape considering how bad it was. The neck of the tank is indicative of what the whole tank was like, and now it looks like there's just a few stray spots of rust here and there. You can see how bad the pitting was/is inside the tank.
The seals in the petcock looked like they were trashed so I just left the petcock on and turned it off while it soaked. The petcock leaks now, unsurprisingly. It probably wouldn't have lasted that much longer anyway, but if you're thinking about using evaporust in a tank with the petcock on keep in mind you'll probably need to replace the seals.
