Abstract: An anti-siphon check valve assembly 20 has an upper portion 4 body housing with a shut off seat 9 or seal 6 and a lower portion 3 body housing for attachment to the upper portion 4 body housing. Inside the body housing is an internal float 5 and a compression coil spring 8. The internal float 5 has a shut off seal 6 for engaging a shut off seat 9. The compression coil spring 8 for biasing the internal float 5 to a shut off position wherein the seal 6 engages the shut off seat 9. The check valve opening force is less than 1 psi, preferably less than 0.5 psi, more preferably 0.25 psi or less. The anti-siphon check valve assembly 20 also has an “O” ring seal 7 to seal the upper portion 4 of the body housing to the lower portion 3 of the body housing. The shut off seal 6 can be made as a washer gasket.