First you need to know what do you want to extrat in the disicator, if you want take away water, check what is the easy way to extract the water, because the vacuum it is not easy and check the safe condition of having a device on 0 kPa pressure.
I will place the metal powder inside the desiccator and suck the pressure inside the desiccator until it reach the minimum value of pressure which is in vacuum condition.