If you suspect your drain line is clogged...
Connect a shop-vac at the end of the drain line outside
The end of the drain line is usually located near the condenser. Make sure the connection is sealed so that you get the maximum suction from the shop-vac.
Vacuum until there is nothing left in the line
A few minutes of suction should suffice, but verify that, if there is algae or water in the line, it comes all out.
Add a cup of bleach at the start of the drain line inside, on the Air Handler
Be as cautious as any other occasion handling bleach. The line will most likely be covered by another piece of PVC. This cap should not be glued on, so you'll be able to remove it by shifting it a couple of times.
Dry off any sweat or condensation on your drain pain, under the Air Handler, if you have one
Use an old towel or rag to dry off any extra condensation.