How clean an enamel bath tub?

[NA Foster]

How can I clean what looks like several years build up of soap scum on a enamel bath tub?
I have tried several commercial cleaners but it looks like it will be days before it's done.

[Account Closed]

I googled it and found this, along with other sites. At a glance, this one has several solutions.
http://www.wikihow.com/Clean-Tough-Stains-from-a-Bathtub

I found a really good toilet bowl cleaner at ACE Hardware, I think. About a quart, in a white plastic cylindrical bottle with blue print. I looked for it at Home Depot yesterday and did not find it, so I'm sure it was ACE. Worked wonders on the nasty toilet that was here when I moved in. That might do the trick. Directions for stubborn stains were to flush the water out then squirt this stuff on and let it set overnight. Worked like a charm.