Gas and Oil Home Heating Furnaces - Tube stopped up

Yes I have a problem with my condensation tube stopping up. It is a Carrier heat pump with electric backup which is in attic. The tube that has the trap in it clogged up about 2 years ago and the way that I found out is a wet spot in ceiling so I called A/C repair and they came out and unclogged tube and charge almost $60. I didn't know it was the tube off the furnace until after he repaired and told me. Well it did it again yesterday and I noticed by the wet spot on ceiling but this time I unclogged myself which is good but the bad thing is I have to repair ceiling again. I would just like to know is there anything you could do to keep it from stopping up or should I just go up there every year and try to blow it out. This furnace lays on it's side in attic and the tube comes out front and runs down in between the wall to the basement drain. Thanks for any help or suggestion's. Steve

pour bleach into the drain line every few months during the summer. this will keep algae from growing in the trap and stopping up the line