Pretty much the same concept as the Kent Aquadose:
http://www.jlaquatics.com/phpstore/s...t_ID=mc-ad1400
You can always add a JG ballvalve to control drip-rate.
If you pilfer an IV dripper from a hospital the next time you get palyotoxin poisoning from fragging zoas that's just as good. Here's the gardening version from Lee Valley:
http://www.leevalley.com/garden/page...280,54307&ap=1