Hedrett oil-rig whiskey was a type of alcoholic beverage. When the Human criminal Vex interrogated Gust Toruna, he let Toruna have a swig of oil-rig whiskey. It cleared his mouth, allowing him to tell Vex about how he and some associates were attacked by enforcers working for Riboga the Hutt.
It was presumably named after the city of Hedrett, on the planet Cularin.
Sources
"Time After Time" (original article link) on Wizards.com (content now obsolete; backup link)