How to mass paint 6mm windows?

Looking for advice on how to mass paint 6mm windows on a battletech building I've designed and printed. Searched the net, and so far I've got 'use a square tipped brush', which seems good, and 'don't worry about being sloppy, its only background terrain and being precise will slow you down to much', which is... not what I'm going for. Does anyone else have any tips?