The most fundamental - but sometimes ignored - step in replacing buried downspout lines is to ensure that you haver a negative grade for your lines to conduct water via gravity.
Mark Your Path
Before you dig call PA1 Call to make any underground utilities.
Using the right equipment will ensure minimal yard disruption.
Proper and Professional Fittings
Heavy duty piping should be used to ensure the system will last.
Cutting the end of the pipe to the profile of the earth is just one of the details you get with a good company.