Get a nice new sponge. That works pretty good in my setup. When I need a kick of moisture, I wet it, wring it, and stick it in the corner. It lasts for quite awhile and if I need to re-wet, a couple well aimed squirts from a spray bottle and back in business I be.
It's square, around 4.5 x 6.5 ..............y'know, basic cleaning sponge. Or go to bath and body works or something and get a fancy one......whatever suits ya