I have a couple of sanke kegs that I'm going to use as fermenters. I've removed the stem and I'm going to clean them with oxiclean. I've had the kegs since 1997 so I'm sure they need a good cleaning. I put a couple of gallons of solution in and sloshed it around. To get the sides I put the keg on its side and rolled it a few times. Is this enough to get it clean? How long should I soak it?