pour into the pump resevor and when the water level gets to the dump stage the float will activate the pump and the bleach water will circulate through the lines and then out to the dump area outside the house.
I do this on a reqular basis monthly and have not had any problems. during the winter when the pump does not activate, I put a few teaspoons of bleach into the resevor to also kill the growth.
No problems to date, but good heads up. If still concerned, contact a plumber for something that does the same buy maybe more friendly. I was told this by the installing plumber who rerouted my condensations lines on the indoor unit to by pass the reg way and detour to the pump.