This is a rain leader and its purpose was to collect rain water from the roof and deposit it into either the municipal storm or sewer system. Any rain leader that has its own line (two sewer caps/plugs at the front of the house), normally drains into the storm system and it is considered to be obsolete. Over the years, we have come across countless examples of people unknowingly using the storm system for their washer discharge, bathrooms to whole houses. Removing or capping access to the storm line will negate a backup threat from the municipal storm system.
Call Jay’s Sewer & Drain Service if you would like yours removed and/or capped.