gotta have fill valve, a chamber, a ball valve, and a breech loading barrel.
http://www.spudfiles.com/forums/viewtopic.php?t=310
for ur handle, either buy a toy gun and clamp it on, or use a "Y" fitting, but because you are using a ball valve, it will be difficult to use it as a "trigger"
make sure u use pressure rated parts, and figure out how to connect all the peices correctly, solvent weld them good, and make sure it has no leaks. make one, test it, if u have problems, then tell us.
"whoa... I thought pimpmann was black..."-pyromanic13