A fitting for injecting a first fluid into an injection port of a cable accessory. The fitting includes at least one seal positioned on an injection nozzle. The nozzle is configured to be inserted into the port and has an internal fluid passageway through which the first fluid is injected into the accessory. The seal forms at least one fluid tight seal between the nozzle and the port. The fluid tight seal prevents the first fluid from exiting the accessory and flowing into an outer portion of the port and prevents a second fluid from flowing into an inner portion of the port. The first and second fluids have first and second voltage potentials, respectively. The second voltage potential is different from the first voltage potential. The seal isolates the first and second voltage potentials by isolating the first fluid from the second fluid.