Which cast-iron repair method utilizes an injection gun for sealing?

The method that utilizes an injection gun for sealing in cast-iron repair is anaerobic sealing. This technique involves using a specialized adhesive that cures in the absence of air, which is key for effectively sealing gaps and leaks in cast-iron pipes. The injection gun allows for precise application of the anaerobic sealer into the repair area, ensuring that the sealant is correctly positioned to fill voids and create a reliable seal.

In contrast, flange welding involves melting and fusing materials together at the flanges, rather than applying a sealant, which does not involve an injection process. Mechanical sealing employs physical components to create a seal, typically using gaskets or other types of mechanical fasteners, but it does not utilize an injection gun either. Cap sealing focuses on sealing the ends or caps of pipes but again does not use the injection method. Thus, anaerobic sealing is the distinct option that aligns with the use of an injection gun, making it the correct answer.