Plumbing - Drain Primer
Has a vacuum breaker, ie air gap, as part of the unit.
Mount it more than 6" above the top of the drain. Need to have a downward sloping pipe to the drain.
About $39.95
http://www.pexuniverse.com/sioux-chief-prime-perfect-trap-primer-valve-695-01
http://www.pexuniverse.com/docs/pdf/sc-695-br.pdf
http://www.pexuniverse.com/docs/pdf/sc-695-specs.pdf