Why are backwater valves not available?

[Fusion916]

I want to replace my existing backwater valve with a new one and extend some abs pipe to run a drain for my washer machine.

Why do places like home depot not sell these in the store?

http://www.homedepot.com/p/NDS-3-in-ABS-Backwater-Valve-375/100128063#.UgE_c5JllHA

And they not really used anymore or something?

 

[johnjh2o]

They're not a stock item. Maybe one in a thousand homes would have a need for them. Not many plumbing supply houses stock them but they can be ordered.

 

[LiQuId]

also technically you are supposed to be certified when installing or maintaining these, my course was a Veeeeery loooong and boring 2 days.