Drainage field? I smell DWV. Make sure before you build anything that the pipe you have is rated to the pressures you want to run.
Unless you have a lot of tinker time, a ball valve just might be a better approach than trying to make a piston valve. Either way, you also might want to think about having threaded fittings so you can change out the valve or barrel.
If you do decide to build a piston valve, there are tons of tutorials all over this forum, on http://www.spudfiles.com
and other websites. Let your fingers do the walking.