Abstract: A marker post system for marking the location underground pipelines includes marker post holder which removably holds a marker post. The marker post holder is configured for releasable connection with an underground tube. Removal of the holder from the tube provides manual access to the interior chamber of the tube to facilitate cleaning the interior chamber and removing a broken segment of a marker post which otherwise would be difficult without digging up the tube. A substantially watertight seal is preferably provided between the holder and marker post to prevent water from entering the interior chamber of the underground tube.