How do I bridge two wired DD-WRT routers?

I was ready to give up and go back to stock firmware when I discovered a well hidden tip in the dd-wrt.com forums about Rosewill RNX-GX4 - Advertised as DD-WRT Compatible that instructs:

You could simply enter DD-WRT firmware and : go to "vlan option", uncheck the “W”column, then "save" and “apply”, then check “W” again then "save" and "apply" <====this could solve the WAN isn't work.

I tried exactly that and it solved all my problems.