I just instsalled a new section of 4 inch pvc drain pipe. One connection is dripping. Is there a way to seal it without a re-do?

Yes, several things come to mind. If you're going to have a leak in a pipe joint a drainage leak is the easiest one to fix. You can wipe off any moisture and paint the joint with primer, making sure that the primer gets in the crack of the joint. Now slather glue all around the joint, forcing the glue in the crack. Let dry and test. Another way would be to caulk the joint with JB Weld Good luck, Tom