I used to use an old toothbrush, but that caused minor scratches. Now I use a scrap of microfiber wrapped around a plastic razor blade with a little QD.
these work well (use it with some QD), but you got to be very careful so you don't scratch the paint. they're discontinued, but type in " meguiars triple duty detail brush " in your google search, and you can still find them for around $3...
p.s. try taking a toothbrush and cut a few rows off...