My Grandfather used to sing us a version of this tune, I am trying to find a recording of it, I have only ever heard his version. Here it is..

Chorus:
Ridin' on a hump back mule. Ridin' on a humpback mule.
The only song that I can sing is ridin' on a humpback mule..

Well I went to see my gal last night, thought I was a sneakin'
I kissed her nose instead of her mouth and the dog-gone thing was leakin!

Chorus

Well I thought I'd marry a skinny gal but I tell you what she'd do
she'd pull the plug in the bathtub and she's liable to go through!

Chorus....