Built one this weekend, about $20 total and 5 minutes of "labor"
Great idea and thanks for sharing
(I agree about the trigger, you don't really need it since your faucet/cobra tap handle essentially becomes the new trigger)
Also, knowing that a Firestone liquid post works on a 3/8" flare fitting, that opens up a lot more possibilities for other "creations" and tools. Like this:
http://www.chicompany.net/index.php?main_page=product_info&cPath=375_19_221_226&products_id=892
You could put a corny post on this and then hook it up to a water line for cleaning/rinsing/etc.