A few years ago I was living in a home where the air handler was up in
the attic. I neglected to ever maintain the air handler's drain pipe
so it eventually clogged up and started leaking water down through the
bathroom's exhaust fan.
That unfortunate experience taught me to check, clean, and flush out
the pipe at least once a year. I took pictures of the process this
time and created a quick guide.
Here's the gallery page -
A wet/dry vacuum makes the procedure easier, but just flushing out the
pipe with water is usually enough to keep the pipe clear.
Ft. Lauderdale, FL