So I scrape the junk off with a screwdriver, then take a wire brush to it. Funny thing, after wiring brushing, there was still a dark spot. So I took my trusty tool box dental pick to it. WHOA! This tank needs a dentist.... bad. So I scrape the junk off with a screwdriver, then take a wire brush to it. Funny thing, after wire brushing, there was still a dark spot. So I took my trusty tool box dental pick to it. WHOA! This tank needs a dentist.... bad.