I do it much more simply:
I remove the ball lock gas fitting from the gas hose on my CO2 tank, stuff it down the PET bottle and fill with CO2. Then dump in one pound of hop pellets. Cap with the carbonator cap and fill to 15psi CO2. After I open the bottle to use some of the hops I again stuff the hose in the bottle, gas it, then cap and give it 15psi. Been doing this way for years and works great.