To create a siphon, you need to have to coolant inlet at a point of very high velocity airflow. The high velocity causes a low pressure, which "sucks" the coolant into the airflow (Google "Bernoulli effect"). This is typically accomplished by creating a venturi in the airway.
However, for coolant, a "FogBuster" setup is inifinitely superior to the siphon approach. The patent is here, and is easily home-built:
Coolant spray system - Google Patent Search
A FogBuster will provide a virtually invisible, ice-cold mist with enough airflow to efficiently clear chips, and requires very little air (I'm using a $79 compressor) or coolant (I've been working for 5 years on my first gallon of coolant concentrate, and I've still got about 1/2 gallon left), and makes virtually no mess when properly setup (perhaps a few teaspoons of excess coolant on the machine at the end of an 8-10 hour day).