I use Tremclad and rolled it on, works very well covers in 2 coats. I've seen some use Krylon spray but it takes a few coats and you have to tape off the rest of the tank and have a place to spray it. I wiped down the glass with thinners and let it dry before painting so it would stick well to the glass.
I used blue on my old tanks and used black this time and love it.
Here is a pic from 6 or 7 months ago.
