a country blumpkin is a variation of the blumpkin, where the recipient of the head giving is sitting in an outhouse instead of a toilet (and the person performing the fellatio is usually a sister or a cousin).
Cletus: "Ellie May, come out to th' shitter 'n give me a country blumpkin!"
Ellie May: "Well shit, I already gave Paw a country blumpkin! You'll have to wait 'til after supper!"
A country blumpkin is similar to the well known, but more boring, blumpkin except it takes place anywhere outside. The act is receiving a blowjob while dropping a deuce with the added bonus of enjoying the great outdoors. The quintessential country blumpkin would involve a cousin and a corn field.