I recently have done battle with
rats in my garage. Since usenet
was a big help to me, I thought I'd
summarize what worked for me and
what didn't. I hope this info helps
someone in the future.

The biggest problem (to me) is that
rats carry many diseases, most unpleasant,
some fatal. This fact alone may lead
you to retain a professional exterminator.
Unfortunately, it is my belief that exterminators
don't *kill* many rats, but just
drive them away. My infestation closely
followed an episode where my neighbor
had a rat problem and hired an exterminator.
I think they just moved up the street.
So, if you go this route, you may not
be doing any favors to your
neighbors by hiring an exterminator. If you DIY,
then, wear a respirator and gloves, and wash
your clothes thoroughly and
often. I used a mix of bleach, ammonia,
and soap and water daily.

IMO, traps by themselves are basically useless.
Rats are cautious, and are pretty
smart. At the least, if you use traps,
bait them but don't arm them, so the rats
become comfortable. Then arm them
and you may nail a few if they are optimists.

The traditional approach is poison bait. The most
common poison is warfarin, which
is an anticoagulant. Unfortunately, rats
evolve very quickly, at least metabolically, and
have become resistant to warfarin. I had
absolutely no food in my garage, but I found that
the rats had made their nest in an old box of
DCON warfarin-based rat poision (?!). A more
modern poison uses bromethalin, but I am
afraid rats are adapting to this, also. Bromethalin
attacks the myelin sheath on the nerves (like polio).
I never got bromethalin to actually
kill a rat, but it slows them down so
that other approaches become more effective.

Rats will take the bait back to their nests
and hoard it, so I would recommend using cubes
of bait (rather than loose grains) and then
leave some cubes loose (for rats to take home)
and fasten some down, so they are forced
to eat those in place. After a few days, I began
noticing rat tails in my driveway. The
local predators were having a field day with my
wacked-out rats. Also, my traps began
to work as the rats were becoming disabled.

It seemed like the really big rats could tolerate
the bromethalin the best, and never really
slowed down that much, but at least by
that point I had interrupted the life cycle
by nailing the pups. At that point I played
my ace, which is antifreeze. Rats apparently
like the smell and the taste. The largest
rat literally keeled over while drinking antifreeze.

I have been rat-free for a week, but
have no delusions that the war is over.
At least I
won the opening round. I will be
looking for additional poisons, beyond the bromethalin
and antifreeze, and I plan to experiment with electrocution.

In summary, I would say:

*lead off with a bromethalin-based poison
*keep rebaiting, and after a few days introduce traps
*at first, use the traps unarmed, to breed familiarity, then
*arm the traps. Continue to bait. At this point, warfarin
may be of some use on already-weakened rats.
*after a week or so of poisoning, introduce antifreeze to
hit the biggest ones.

Then, clean up thoroughly. No food available at all. Close up
any possible access points. Leave out bait blocks as a tell-tale.

What a drag.