The correct phrase is "He couldn't pour piss out of a boot with the instructions on the heel."

Our here in The Real West we don't use none of them namby-pamby bedroom slippers. Black Nate did, once, in the bunkhouse, and Cosi thought Nate's feet had been devoured by bunny rabbits and so Cosi liked to beat them feet to death before cooking them up as rabbit hash.

No sir. We wear good honest socks like God intended, or pull our boots on to go to the outhouse at night.