Dubbin is a euphemism for masturbating a penis, specifically the rubbing of the shaft of an erect penis, until the glans has an eruption and the volcano spews forth millions of wiggly creatures from beneath the surface mixed in with a glob of what may appear to be tapioca or pancake batter, depending on the health of the dubbiner.
Oddly enough, that same motion can be used for the other definition of dubbin, which is a mixture of oil and wax used on leather products, especially shoes and boots, to condition them and make them waterproof and flexible. All kinds of wax can be used, from bee's wax to manufactured ones. The oils can range from fish to mink oil, tallow, even lard. The general idea is to use the oils to condition the leather and the wax helps them to become waterproof, especially around the stitching.
If you happen to own a leather dildo, you can combine both of the above and be pleased with your ability to multitask.