Wash as in cash. Scottish comedy vernacular describing cunnilingus, with particular emphasis on the moisture caught and remaining on the face of the person administering the act.
When you take a very small smart car and the largest southern woman you can find and make her bend over, exposing her anal cavity, then drive the smart car at maximum speed into her anus.
I just bought a new smart car, the first thing I did was a swaberdash.
a slabber dash is what happens when jamie farts. his buttcheeks ribble together making a noise that sounds exactly like a machine gun firing baked beans.