Today in my shed... I have been making a dip tank for cleaning off rust, paint, grease and dirt from bits of machines. It's just an old oil tank with the top hacked off, the drain holes blocked off, the bracing inside removed and a rib fitted round to stop it bellying out. Nothing special... This is a sewage pump that I had to repair. The pump sat in a bucket of caustic soda/water mix for a few days, taken out and rinsed off, dried and then given a light wire brush, 10 seconds worth. It eats grease, oil, paint, rust and dirt, skin and eyes, so you need to wear goggles and gloves and waterproofs and keep kids and animals well away. It doesn't touch iron based metal, but eats copper based alloys. Aluminium is not to go in at all, it dissolves quickly and it releases hydrogen gas which could go with a bang. I've only started using it, played a little with the caustic/water ratio and heating it, but I think it's great stuff (again, treating it with respect) Has anyone else used it?