What is the best way to install a sump pump discharge line?

It should 1)Be able to still operate if frozen or clogged 2) Be uncoupled as to allow for frost heaving 3) Have an air gap for venting and freeze relief.

Other things to consider....
Using schedule 40 holds up better than thin wall over time .
3" is okay but 4" is best.
Sump line should run downhill to final discharge.

If your sump is in a finished basement... A battery back up is okay but will only last so long. Water pressure operated pumps may not keep up. A generator would continue to power pump(s) in the case of an extended power outage.

Remember.... The first and best way to keep water out of you crawl space or basement is to ensure your gutters and downspouts are working properly and getting water clear away from structure. Secondly, check the soil grade... that is slopes down and away from house.

I have witnessed flooded basements and crawl spaces on numerous occasions. Keep in mind, if your basement or crawl space floods, will it ruin your water heater, furnace, or other expensive equipment?

This is why sump pumps and discharge lines can be so critical.