If your pump casing is just dirty, it should come up pretty good with warm water and detergent. If it's corroded/oxidised then it will need something more aggressive, maybe a good starting point would be a careful application of oven cleaner. I think the biggest hurdle to soaking the outer casting is being able to separate the inner parts, one of the bearings is difficult to remove.
I've still got to do mine, although the look I'm after is unrestored rather than just-off-the-line. So will be following this for tips!
