When using designline, wouldn't it be nice to have a button or command to fill unfilled inactive designlines without double clicking, activating and selecting the Fill3D button? Use the command FILLOBJS. This will allow you to select any designline that is not active and fill it in with the last service that was used. Make sure to select the design line once you run the command by left clicking. FILLOBJS works with multiple designlines no matter the discipline.