Disclosed herein are check valve assemblies with enhanced back flow protection. There are at least two duckbilled check valves, each having an inlet at one end and an elastomeric bill formed at an opposite end, the bill having opposed lips and an outlet openable by a flexing of the lips apart. The bill of the first duckbill check valve is telescoped into and retained in the inlet of the second duckbilled check valve (e.g. by a jam fit or snap fit connection). These assemblies can be positioned in compact conduits such as those found in garden hose outlet nozzles.