Air Conditioning - repeat rust clog in central a/c condensation line

We had water leaking from the bottom of our a/c. We cut the pipe that carries water away from the air conditioner, and there was a piece of rust clogging it. We flicked it away with a screwdriver, but it looked like there were smaller pieces of rust in the water, too. We redid the pipes, connected them to a pump that takes the water out of the house, and had no leaking for 3 weeks.
Now, another leak, I assume same problem. Can we flush out the rust so that we don't have to have a repeat of this every few weeks? How? Should it be rusting when it is only 4 yrs old? Thanks, Jkm

The rust can be coming from either the drain pan or the side support panels on the coil. If it is the drain pan, replacing the pan with a stainless one will cure the problem. If it is coming from the coil support panels, other than making sure the pan is not holding water there isn't a lot you can do. The piping is plastic I presume. If not, replace it with plastic. Any galvanized or black steel fittings are just asking for rust troubles.

Hey, check out this thread http://forum.doityourself.com/showthread.php?t=311234 I've never had that problem before in 19 years, then it happened twice in a few days!