Internal duck bill to fix leaky scupper

Did some searching and found a lot of info on small plug style duck bill valves and versi plugs. Versi plugs look great however the they inhibit flow. Has anyone used a 2" insert able duck bill valve to stop a scupper from leaking? Duck bills seem to be a cheaper option without sacrificing flow rate. My main concern is that the rubber will be too rigid to open unless the engine compartment is full. Wanted some input before I try it out.

http://www.duckbillvalve.net/products/63.html

This would be better however haven't found any in 2 inch:

http://www.tideflex.com/tf/index.php?option=com_content&task=view&id=257&Itemid=388

Ebay version for vacuum pump. Looks even more rigid than the first two:

http://www.ebay.com/itm/385311208-S.../221431093354?pt=BI_Pumps&hash=item338e52586a
 
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