Our former home had the HVAC air handler installed above the ceiling in the attic.

The condensation drain pipe that allows water to flow from the air handler's drip pan to the outside of the home had become clogged with fungus, mildew, algae, debris and even small plants.

Once the pipe was clogged, the air handler's evaporator drip pan overflowed and water began leaking down through a bathroom exhaust fan.

A yearly cleaning regiment could have prevented the clog and the subsequent water damage to the ceiling.

I've started using some HVAC cleaner at least once a year to keep things working properly.

If there is no access cap, you may need to unscrew part of the PVC pipe in order to be able to flush out the line.

If you'd like to skip the pipe flushing step, you could just find where the drain pipe terminates outside your home and suck out any fungus or debris with a powerful wet/dry shop vacuum.

I let the vacuum run for about 30 seconds, turned it off, and checked the results inside the vacuum's container.

There was a small amount of water and a few small bits of fungus inside the container.

If your condensate drain was clogged, you should see substantially more water and algae, fungus, mold or slime inside the container.

You can also try moving the wet/dry vacuum's hose to the "blow" side of the machine and send some air through the pipe to force any remaining obstructions to the outside of the home.

If you still feel that the pipe may be clogged, find the exit point of the pipe outside the home and vacuum it with the wet/dry shop vacuum.

If you're lucky enough to have an air handler equipped with an overflow sensor, you won't have to worry much about water leaks.

When the condensate pipe becomes clogged, the drip pan fills up and the sensor turns off the air conditioning system.

I waited for about 30 minutes to allow the bleach to kill any microbes living inside the pipe and then flushed it out.

To flush out the line, I refilled the empty 1 gallon bleach container with water and poured it down the drain pipe access hole several times.

I didn't want to leave any bleach sitting in the drain pan or the the PVC pipes since I've read that bleach may cause damage to any metal pieces, the glue that holds the PVC pipes together, and the PVC pipes themselves.

Just in case, I checked all around the HVAC air handler unit and and the drain pipes looking for any water leaks.

My last step was to mark the calendar to repeat this procedure next year.

If you live in an especially hot and humid environment, you may want to check, clean, and flush out the condensate drain pipe at least twice a year with some HVAC drain cleaner.