Another vote for Oxi-clean. I used it to clean red wine out of a glass carboy once and I was surprised at how well it worked. I don't think we had a brush, so we just threw in a couple scoops of Oxi-clean and filled it to the brim with water and after a couple hours, the stains (little dried-on drops of red wine) just released and floated to the top.
We had tried a little bit of soap and water, and shaking it around, then bleach and water shaken around, and they didn't remove any of the stains. The Oxi-clean was a last resort, but worked great.
(One may consider it a waste of 5 or 6 gallons of water to fill a carboy full just to soak it, but if you're trying to save a dirty one it's worth a shot).
Weldless? Why would anyone want to weld less?