Whitewashing literally means applying a wash (which is white, typically being lime or chalk) over a surface. The wash covers whatever was underneath with a uniform coating that hides what's underneath. It's like paint, but ancient.

Whitewashing has been a thing since before races (which are biologically meaningless) were called colors.

As a metaphor, it means exactly the same thing -- hiding the parts underneath with something that covers them.

Whitewashing is not sanitizing. Sanitizing something actually fixes it. A whitewashed surface is not implied to be sanitary. Lime is basic (high pH) so it also discourages (eg) mold growth, but it's not sanitary.

More generally, not every word that includes the substring "white" is a part of the conspiracy. Whichever conspiracy you are demonstratively opposing here.