Joe, I use a bulk eraser for my decks, some folks prefer a wand type. Ther are three very important things to remember when de-maging...
1. Remove all tapes from the room, preferably several rooms away.
2. if the unit has a switch, be at least 3 feet away from the heads when you turn it on, move slowly towards the heads and pass the unit over the head area for a few seconds, Do Not turn it off! Move slowly away back about 3 feet then switch it off or unplug it
3. Do Not touch the heads with the unit!! Ever!
I do cassette decks every 6 months, RtR's every 10 plays or so. I bought the bulk one so I could do tapes as well as the heads, very powerful, but it doesn't erase metal tapes, not enough gauss power for them.