What's the difference between foot-washing Baptist and Baptist, as mentioned in "To Kill a Mockingbird"?

The term "foot-washing Baptist" is used in Chapter 5 of the novel to describe both Boo's father and Nathan Radley, Boo's brother.  Here is the quote from the novel:

Miss Maudie settled her bridgework. "You know old Mr. Radley was a foot-washing Baptist-" 
        "That's what you are, ain't it?"
        "My shell's not that hard, child. I'm just a Baptist." 
        ....
        Apparently deciding that it was easier to define primitive baptistry than closed communion, Miss Maudie said: "Foot-washers believe anything that's pleasure is a sin. Did you know some of 'em came out of the woods one Saturday and passed by this place and told me me  and my flowers were going to hell?"

      Scout is at first confused, thinking that foot-washing means what it says.  However, as Miss Maudie explains, it is a reference to a strict adherence to "cleaniness" of the soul.  As humans, we should not experience pleasure, for that takes away from God's power and our worship of him.  A "just" Baptist, like Miss Maudie, is a Christian who follows Baptist rules, but believe that it is ok to take in pleasure in the experiences of life.