A Double Tap bushing is a fitting widely used in petroleum operations.
The bushing is flat, round fitting. It is threaded with an insulator on its outside circumference. In the center of the fitting is a threaded hole. This center hole is threaded in two directions, top and bottom of the bushing, usually made dielectric to isolate these fittings when in use.
Double-tap bushings are fittings inside oil tanks, like the double-bottomed installations in refineries.