Dec 2005
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I just went through this on the 57. I first used about 1 lb of TSP
 mixed with hot water, and filled it up. I let it sit a couple of 
hours, drained a bit off, added a couple of short lengths of chain,
 a hand full of big bolts, and shake it throughly. Then drain, and 
rinse. That got most of it, but not all. I then used Red Devil Lye 
and hot water, letting it sit about 4 hours. It got hot, it got shinny
 clean. Rinse repeatedly, blow dry, bake in sun for a day, and mount.
 I used a water away product on the first fill up to be safe. Now, I 
am no chemical expert, but I have been a plumber for 28 years, so I 
know about "drain-o" type products. They can be dangerous! Please use 
caution, read the label, wear protective gear. "Drain-o" is generally 
lumped together like body fillers are lumped together as Bondo. "Drain-o" 
type products are acidic. The Red Devil Lye is alkaline. Use extreme 
caution with each, they can burn, a chemical burn you will not like.
I would recommend to use the lye, Red Devil is the only readily available
 lye around these parts. Stay away from the acid products (for drains and
 shop use). Of course, the radiator shop may be an economical option.
(from Stde Tech talk)