Here is an interesting way to remove the built up algae water in your system.
Might be very useful to approach it this way. In addition (from the inside of your house) the condensate drain line is usually a PVC pipe that takes the water from the drain pan to the condensate pump. Disconnect the PVC pipe (pliers). Frequently, there is a valve connecting the pipe and the pan. Pour bleach into the pan and through the PVC pipe to destroy the algae.