Using only one household item, HomeTips4You shows how to "Clear out all the gunk and the funk within that AC drain line" cheaply and easily. To try this hack at home, first turn off the thermostat.
An air conditioner ... the line or suck out the clog with a wet-dry vacuum, followed by the application of a liquid PVC pipe cleaner. A DIYer can also snake out the drain line with an AC drain ...