I have seen bleached used. Pour about 1/2 cup inside the condensate p-trap to keep the condensation drain pipe from clogging with debris ( materials similiar to that on a lint filter of a dryer, accumulates in ac drain pipe. ) To prevent the condensation pipe from clogging , use a little bleach each season poured into p-trap of pipe ( near the indoor ac coil) . If the pipe clogs up , then the excess moisture/ condensation water does NOT DRAIN out, then it holds heat from water & can cause the ac to seriously malfunction by not cooling . Its preventive maintenance. Or wait for it too clog and have a ac repaor person come easily unclog the drain for $150-400!! good luck.