I’ve been thinking about this idea for sometime. It never fails, I’ll need to fill a gun in the middle of the tank being filled. Or I hate having to waste the compressed air that’s in the dryer canisters every time I want to fill two different bottles. Now with adding a tee fitting and a needle valve. I’ll be able to open and close the valve. Allowing me to continue to fill on both ports at the same time or switch back and forth between the two ports with out stopping the compressor. It would be nice to have two needle valves to do this job. But I should be ok with one. I’ll just not be able to remove one of the tanks until I’m completely finished with filling all the devices. But with use of the tank valve, I’ll still be able to isolate between the two. And fill either one. It wasn’t to badly priced, I spent about $55 on everything. The 6000 psi valve was most of the cost.