We used to have issues with viper and nanoviper lines but now we use a torque screwdriver (H4DETSD) with a hexagonal adaptor bit with a cutout for the line to tighten the lines to ~30 cNm and ~20 cNm for metal viper and glass nanoviper connections respectively. We also do a near fully connected leak check with a pre-detector plug (closed system). This has resolved all viper tightening leak issues for us.