Abstract: An improved floor drain for buildings, basements, exterior paved areas, and the like. The invention provides floor drain assemblies and check valves providing improved drainage performance, particularly where drainage is an irregular occurrence, and having unprecedented simplicity and reliability. Floor drains according to the invention comprise check valves adapted for disposition within floor drains, the check valves generally comprising spring-loaded stops or elastic diaphragms, either of which may be tailored for opening under a selected hydrostatic pressure. Use of the check valves according to the invention permits drainage through the drain conduit while preventing back flow from the drain of undesirable or unwanted gasses. Check valves according to the invention are preferably installable in existing drain structures, and easily removable for maintenance or replacement.