Seal up the holes with some roofing sticky tape and plastic, wipe down the rubber seal and cover it with vacuum oil. Pour desiccant in the bottom of the pressure cooker, add items to be dried.
Affix the lid to the pressure cooker, then affix the vacuum line going to the vacuum pump. Set the pressure cooker on a hot plate and turn to the lowest setting.
Pull as much vacuum as your pump can handle and let set for a time determined by the thickness and amount you need to dry. A small pickle jar full of sample will take a few days to fully dry, spread out the sample on a sheet of aluminum foil to speed the process.
Do not leave unattended while heat is on. Your samples will continue to dry if you pull at least 25 inches of mercury even without the heat on.