Video using the green earth injector about half full of soap with my foam gun: http://www.youtube.com/watch?v=HXIeXq20Btk&feature=youtu.be
I'll update later with better soap, higher psi air, and a video in the day.
This is to keep the soap suds on the car as long as possible to break up the bugs. I was playing in the garage one night. I have seen compressed air car wash foam guns that are $100+ , compressor foam cannons which are $100 or so, and foam hose guns that are $40-$60 First I though use a harbor freight cheap car paint gun with soap in it. Harbor freight was closed to try it. How do you get compressed air out the end of your hose sprayer? Think one way valve; so I made one. Here's how. The video shows using air at about 40 to 60psi due to the time at night I finished and not wanting to turn my compressor on and piss of the neighbors. Higher psi would probably produce more foam, esp if it had a chamber or hose between the chamber and hose y connector to mix the soap and air in more prior to ejection. Notice the 1/4" hose coming out of the hose Y. It's the air flowing against the current of the soapy water from a injection device = Green Earth G-Clean High-Pressure Detergent Injector for Pressure Washers that was $15 Model #: AUN31024D. see later pics.
Too bad I later found a $20 green earth cannon for my pressure washer on amazon that works okay. This will work well if you do not have a pressure washer, but do have a compressor. Just get some Detailers Pro Extreme Foam Soap and increase the air pressure and turn down the water at the hose Y as much as possible with your fan spray so the soap is compressed as much as possible with as little water as possible.
One way Valve attached to half of the green earth soap injector's extra hose from the kit attached to a hose Y connector. To narrow the air entering the hose/soapy water I used a patio irrigation 1/4" hose and a inline irrigation male-to-male connector and shaved down the edges to squeeze into the green earth clear tube so that the thinner stream of air would create more bobbles think coffee star vs Slurpee straw in milk and the size of bubbles then add 100 psi. Then it all comes out of the hose sprayer. I chose the two sprayers because one is a gun for on and off and the other can create a fin fan mist better than the 6-in-one sprayers etc.
All the parts
1/4 inch hose with male-to-male connector shaved enough to fit in the clear hose and seal a little. When you pull on the 1/4"" hose it pulls the connector down the hose and the connection is strong enough to pull hard and have a snug fit. The connector also prevents the air injection hose from blowing out the end of the clear tube. I could not pull the male=to-male connector and hose apart by hand. The irrigation stuff is at lowes and home depot in the patio dripper kit area.
The compressor's one way valve. a male and female compressor valve end, The end also provides a good edge for the hose clampt to compress the clear tub onto it. The inner part to the valve is a wire closet cap over a piece of brass toilet bowl bolt. When water pushes on the toilet/wire closet cap "inner valve" it closes the toilet bolt won't rust and it makes sure that the wire closet cap is aligned correctly to seat well every time. A perfect;y round plastic ball or small marble would work also. The 60+ psi has to be more than my waters' 45 psi for the air to escape and when the pressure is less it closes so water does not go into my compressor tank. You want the air to have to puch up on the valve so gravity also helps close it. Use pipe thread on all the thread of the male compressor part, it was just shredded in this pic after dissassembly.