When painting your bathroom walls, you want your paint job to be neat and immaculate. (And consider using a satin or eggshell finish, both of which are easier to clean than others.) One challenging area is behind the toilet tank. This thin space—usually about 2 inches wide—seems to defy all efforts to paint it cleanly.
Forcing a paintbrush behind the toilet tank doesn’t work: You end up with a smeary ring of paint around the toilet tank and plenty of unpainted areas. And conventional paint rollers are too thick to do the job.
The good news is that you have a few simple, inexpensive methods at your disposal: using a thin roller, making your own DIY paint pad, or removing just the toilet tank. All methods will help you paint behind the toilet neatly and cleanly without too much work.
Source: The Spruce