Per the manual on page 5, the following steps should be taken to prime the sprayer:
1. Place the siphon tube into a container of mineral spirits.
2. Place the return hose into a metal waste container.
3. Set the pressure to minimum by turning the pressure control knob fully counterclockwise.
4. Move the PRIME/SPRAY valve down to the PRIME position.
5. Turn on the sprayer by moving the ON/OFF switch to the ON position.
6. Allow the sprayer to run for 15–30 seconds to flush the test fluid out through the return hose and into the waste container.
7. Turn off the sprayer by moving the ON/OFF switch to the OFF position
The purpose of the above is to remove the test fluid that comes with all new sprayers. This fluid must be thoroughly cleaned out of the system with mineral spirits before you begin spraying.
Important: Always keep the trigger lock on the spray gun in the locked position while preparing the system.  If you require further support with priming the sprayer, you may contact Titan at 800-526-5362.