Sometimes, they don't even glue those condensate drains so the piping is easier to clean. Try to unscrew and pull at the same time to see if you can take those joints apart but be prepared as they may come apart suddenly and you could break a piece. If they are glued, you can try to clean the joint area and use a silicon sealant.
Or take it apart cutting as necessary and replace the elbow out of the unit with a tee. Then re-pipe the trap and add a cap to the top of the tee. That way you can flush the drain line and add a bit of bleach on a monthly basis during the cooling season. Use PVC piping like is there and PVC primer and glue.
