THIS IS WHAT YOU DO:
A couple of months ago the EPA told Spartan School of Aero in Tulsa, OK that we can't pour the fuel on the ground anymore. So spartan bought these "GATS" Jars from Sportys. They are big jars that basicly filter out water and other bad stuff. It has a special filter that 'prevents' water from getting through the net. Actually, since fuel is 'lighter' then water it goes through the net first and water is stuck. once fuel is gone water slowly drips through, but by that time you should of stopped pouring anyway.
Anyhow, once you sumped all the sumps, you open the fuel cap and pour it back in until all the fuel is gone. If you feel thirsty at this point you may drink the remaining water.
This is NOT required at all airfields and is relatively a new procedure.
Hope i could help.