I remember seeing where someone had used a basketball or something like that as the "valve".
Held in place with a bungee cord, when you wanna empty it, you just remove the bungee, hit the ball with the end of your shovel-handle...the ball goes flyin & out comes the 'crete.
------------------------------------
Yahoo! Groups Links
<*> To visit your group on the web, go to:
http://groups.yahoo.com/group/papercreters/
<*> Your email settings:
Individual Email | Traditional
<*> To change settings online go to:
http://groups.yahoo.com/group/papercreters/join
(Yahoo! ID required)
<*> To change settings via email:
papercreters-digest@yahoogroups.com
papercreters-fullfeatured@yahoogroups.com
<*> To unsubscribe from this group, send an email to:
papercreters-unsubscribe@yahoogroups.com
<*> Your use of Yahoo! Groups is subject to:
http://docs.yahoo.com/info/terms/