Go ahead and laugh, but if this helps just one person...

Many of us have the small portable air tanks for various tasks, most for quick racing tire pressure changes.  Frustrated by the amount of time and work it was to fill my tank using the "conventional" method I found the common-sense answer.  Honestly, it's only a matter time before anyone would figure this out... I'm quite certain I am not the first.  If you are filling your tank from a compressor, this may help.

Details:

Most portable air tanks use a standard needle valve to fill from.  This is the same type as used on tires, tubes, etc.  The process of filling my 10-gallon tank included holding the inflator to the tank for approximately 3 minutes.  This doesn't sound like very long until you do it.

The new process reduces that time to about 45 seconds and requires no "physical" labor.

Parts:

The only drawback is that you will require some additional parts - they are very inexpensive.

- one female air fitting (not needed if tank is already configured as mine)
- one female butt adaptor
- three male air fittings (two only if tank is already configured as mine)
- Teflon tape
- longer coil-hose (optional)

Procedure:

1. Most portable air tanks come with a premounted hose attached directly to the air regulator.  We will remove this hose to add a standard air fitting quick-connect.  (The long coiled hose is optional, but does allow you to fill both tires on one side of a vehicle without relocating the tank):
   
2. Using Teflon tape, assemble two male fittings to the female butt adaptor:
   
3. Plug the new male-male fitting into the air tank (not the air supply hose from the compressor):
   
4. Attach the air supply hose to the portable air tank.  Release air valve to allow tank to fill from compressor.  (for my 10-gallon tank fed from a 35-gallon 150psi compressor, this took ~45 seconds to reach 125psi in the portable tank):
   
   Note:  Do not exceed the portable air tank manufacturers recommended maximum pressure

Good Luck!

Credits: Skip Grehan