THANK YOU FOR REPLYING, I HAVE A CREPE MYRTLE CALL DYNAMITE. I PLANTED IT ABOUT FIVE FEET UPHILL FROM MY DRAINPIPE IN MY FRONT ROW HOUSE
Dynamite crape myrtle gets 10-15 feet wide. Most of its roots will be within that area. Finer roots will be farthest from the trunk. It should be fine.
Keep in mind that roots do not break pipes, but if a pipe has a break, then roots will find their way in. The roots of crape myrtles are not aggressive though.