A main drain safety grate apparatus utilizes an elongate drain, frame and grate that distribute the suction flow of water over a large surface to avoid full blockage of the grate, and also utilizes a bendable or deformable, upwardly releasable grate that has a section slotted to permit water to drain...http://www.google.es/patents/US6170095?utm_source=gb-gplus-sharePatente US6170095 - Main drain safety grate apparatus
