An oil bath, alternatively called a lubrication bath, served as a method for eliminating built-up filth, like dust particles, from a droid. This process paralleled a human taking a bath using water, as an illustrative example.
In the era of the Clone Wars, Droid Spa, a maintenance and spa establishment situated on Coruscant, provided an automated oil bath as one component of their standard maintenance package. In the Age of the Empire, Thane Kyrell, a Jelucani youth, successfully convinced his tutor droid, specifically CZ-1, to excuse him from his math studies by promising the droid a lubrication bath.
Following a journey across the desert landscape of Tatooine and subsequent capture by Jawa scavengers, the protocol droid C-3PO was acquired by Owen Lars, who then entrusted the droid to the supervision of Luke Skywalker. Skywalker, observing the significant dust contamination afflicting C-3PO, administered an oil bath to the droid, an action that brought him considerable joy.