I use the SIL's, different gun but similar system, works well but it's a fine line between thick enough to last and too thick to spray. We've used a hotplate or propane torch to thin it out by warming which makes a big difference. The long hose with the 360 nozzle is great for inside doors or other inaccessible spots.
The actual commercial gun is pressure fed from an in-tank pump in the 45 gallon barrell and is atomized by mixing it with air right at the nozzle.
I made a sprayer a while ago from a 20lb propane tank. Fill the tank with waste oil or whatever you want. Pressurize it 20-40lbs or so and it'll push the oil thru a hose to a spray gun when it's mixed with air from another hose. Not quite as refined as a commercial gun but it works. Messy as all get out tho.
It claims to waste less Fluid Film and do better job than spray cans
Spray cans aren't cheap then again neither are gallon cans. Once spray cans get 1/2 empty they'll only spray pretty much with the can vertical. You get better more even coverage with a proper gun.
These are all in Canuk bucks at our local Princess Auto, Can. version of Harbour freight. Presently the CAN$ is US$0.75 so the US price is 3/4 the Can price.
Looks like we supply the compressor fitting.
You'd never think there were that many different fittings, none of which are interchangeable. There may be one universal...I
think.