This article is from the rec.audio.* FAQ, by with numerous contributions by Bob Neidorff others.
First, a caution: DAT recorder tape heads are VERY fragile.
Before cleaning the heads on a DAT recorder, get specific
recommendations from a very knowledgeable source that is
intimately familiar with DAT head cleaning. In the internet,
a good source is the DAT-Heads-Digest FAQ. For more information
on DAT-Heads-Digest, see section 20.2, below.
To clean tape heads, use pure isopropyl alcohol and lint-free
swabs. Wipe the metal parts of the transport with alcohol
(DON'T wipe the rollers!) and allow them to dry. Throw the swab
away after use. Be exceedingly careful when cleaning the heads
on a DAT. DAT heads are notoriously easy to misalign by
Practical tape head demagnetizers are available for under $10.
Try to find one with a plastic coated tip. If you can't find
one which is plastic coated. you can slip a drinking straw or
plastic tube over the tip for the same effect. This plastic
will prevent the demagnetizer from scratching the head.
Before plugging in the demagnetizer, remove all tapes from your
working area and unplug the recorder. Hold the demagnetizer
away from the recorder as you plug it in. Slowly bring the tip
of the demagnetizer up to the tape head and slide it back and
forth across each tape head for five one-second strokes. Then
pull it away from the head slowly and go on to the next. After
demagnetizing the heads, use the tip on each metal tape guide
with a similar five strokes. Last, slowly pull the demagnetizer
far away from the recorder and unplug it. Recording engineers
use a demagnetizer before each recording session.