I need to disconnect my head from the overboard pumpout thruhull to comply with local no discharge laws. After disconnecting the hose (valve closed of course) i see a tailpiece is connected with white thread sealant. I wanted to install a screw on cap for safety should th valve leak or be opened in error. How does one remove the tailpiece? It seems to have no flats on it to get a grip with a wrench. The sides of the tailpiece where the hose slides over are smooth also. Any advice would be appreciated.