According to vernal888 :
Hello All:

I'd like to use my 4 gallon air compressor occasionally for spraying paint
with a Wagner Conversion spray gun. Thought it would be necessary to add a
reservoir tank between the compressor and the spray gun. However, the tanks
I find readily available are called "carry tanks" and it's not clear to me
how the connections need to be made. The carry tank has a standard 1/4"
threaded output fitting, but the air intake is a threaded piece that looks
like a tire valve stem and includes the pressure control knob. Advice as to
needed fittings will be very much appreciated.

"Carry tanks" (aka "air pigs") are designed to be filled at the local gas station
off the tire pump, and carried home for refilling other tires... Shrader valve
(tire valve stem) in, hose - shrader valve out.

The ones you see are a bit different.

In my case (shrader in/shrader out), I unscrewed the original manifold from the
tank (1/2" NPT). Then did something like: mount a 1/2" iron tee, with the original
manifold off one leg, and some 1/4" female NPT for standard fittings.

It's usually possible to buy a suitable distribution manifold for not much money,
or, make it out of copper plumbing pipe.

That was the first generation with a 4 gallon "air pig".

The second generation was with a 10gallon "air pig", where I made the new manifold
out of brass, including a home-made one-way valve and pressure switch, and
mounted it on a cart. Turned a tankless compressor into a 10gallon tank type.
--
Chris Lewis, Una confibula non set est
It's not just anyone who gets a Starship Cruiser class named after them.