A boat plug system for automatically sealing a boat. The boat plug system is mounted in a drain hole passing through the boat's transom and includes: a cylindrical-shaped plug; a ball valve assembly removably coupled within the cylindrical-shaped plug; and further comprising a ball, a sealing ball seat component having a frustroconical shape to receive the ball when the ball valve assembly is in the sealed position, and at least one screen; and a plug cap/tool further comprising a tool head on one side for removably coupling the ball valve assembly within the cylindrical-shaped plug and an opposite side of the plug cap/tool from the tool head is for sealing the cylindrical-shaped plug. Water may flow out of the boat's drain hole, but is substantially stopped from flowing from the exterior of the boat to the interior via the drain hole.