I use a small wire brush, shaped like a toothbrush. You can buy them for a couple of bucks at Lowe's, steel or brass bristles. Compared to juices there is no waiting and the brush does a good job.
PS: Somewhere in my mind I asked myself this question as I read your post: What happens when muriatic acid and sulfuric acid come in contact with each other? Is it like when M-acid comes in contact with chlorine?