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Carnation

Plumbing - Drain Primer

Drain primer Sioux Chief 

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

Drain primer diagram 

http://www.pexuniverse.com/docs/pdf/sc-695-br.pdf

http://www.pexuniverse.com/docs/pdf/sc-695-specs.pdf