Can you help me identify this part to my well plumbing?

Hi! My house is on a well and the water comes in and goes through a sediment filter before it heads out to the house. There is a flush valve at the bottom of the clear polyester housing that is starting to leak, so I am hoping I can track down a new clear housing/valve assembly. But, I don’t know what it is called.

Can you look at the attached picture and tell me a name for this thing? Thoughts on a good place online to go for a replacement?

http://www.flickr.com/photos/creativehaze/4329644957/

Thanks!