Gun cleaning should be done as soon as possible after spraying. The longer you leave the paint materials in the gun the more difficult it will be to clean.
Be sure to wear the appropriate protection while handling solvents. Gloves, safety glasses and breath protection are highly recommended.
Remove the cup, air cap, fluid tip and needle. As with any gun you need to be VERY careful when removing the fluid tip. If the wrench slips off it's grip and nicks the tip the gun will not spray properly even with just a slight nick on the tip. With a Sata that could cost you over $150 so hold the gun (any gun) and the wrench securely when you loosen or tighten the fluid tip.
Don't soak the gun body of any gun in thinner for more than a couple minutes and only then when necessary. Use lacquer thinner in a squeeze bottle and a small bowl or cup. Take each part and use the proper size brush to break loose the paint from the walls of the parts then rinse with a shot of the thinner over the cup. You should only need a couple ounces of thinner to do a good job. Wipe the parts with paper towels then lay them on a towel to dry before reassembly. Install the fluid tip on the body BEFORE you install the needle, if you install the needle first you could tighten the adjustment too much and then when the fluid tip is tightened you could bend the needle or damage the fluid tip. Lubricating the needle will help the action of the trigger remain smooth. If you use a decent gun cleaning kit you can push a probe through the air cap holes to help keep them clean. Wipe out the cup with paper towels before you use thinner to finish the cleaning it and be sure to clean the pipe between the cup and the gun with the proper size brush. I usually finish cleaning the cup by dampening a paper towel with clean thinner and wiping it out. Don't leave plastic or rubber cup lids in thinner, it will damage them.
The waist thinner can be either used for other clean up jobs or placed in an evaporation pan in a well vented location so that it doesn't pollute the ground water. If you have a larger quantity of solvent to dispose of you should make contact with a body shop in your area and ask if they would take care of it for you. This could cost you a couple dollars but it would cost you a lot more if your found dumping illegally. Solvent dumped on the ground can be detected years later. NEVER dump solvents, paint or anything else illegally it negatively effects all of us in many different ways and generates laws that take away our rights to use these products.