Vacuum breakers are a safety device required by some municipalities to hook your sinks into the public water supply. It prevents (in the worse case scenario) chemicals in your bowl being sucked back into the public water supply causing contamination. Some places require it and some places do not - check your local building codes. A plumber can usually install the vacuum breaker even if it the shampoo unit was purchased without one - but you will need to specify your item (model) number.
We have a variety of Vacuum Breakers - you will need to specify the shampoo unit item (model) number when purchasing Vacuum Breakers. Please call 1-800-578-8772 for further assistance