My Uniflow generally empties very well unless the powder is sticking to the sides of the hopper.
Get a light and look into the hopper. You will see if there is any powder remaining. A few bumps will generally be sufficient to cause the granules to drop into the cylinder cavity. If the powder is “sticking” to the side of the hopper, I grab a used clothes dryer anti-static sheet and run it into the hopper and make a few light circles around the sides and hopper bottom (I wrap the sheet around a long screw driver or wood dowel to reach to the bottom of the hopper.) The powder will be dislodged and can then be dumped. Cycle the cylinder a few times to show clear.
MOST IMPORTANT: Store that powder before getting the next powder out on the bench!
My measure has never been cleaned. To clean the sucker would remove the graphite coating.
A lack of planning on your part does not necessarily constitute an emergency on my part.