I have a portable air tank. I just put 40 PSI in it to blow out my lines. If I run out of air in the portable tank then I just fill it back up. I have a small TT but, it never takes more then 2 tanks.
I try to keep it below 30 PSI which is lower than most city water connections. You don't need that much pressure to blow them out, and a few remaining droplets won't hurt the fittings.