Just empty the powder, do a visual inspection, reload, and go.
As Unclenick mentioned, you should disassemble the rotor/'drum', if you encounter any binding or see small particles of crushed powder around the edges.
Leaving as much graphite as possible in the hopper, on the rotor, and in the bore of the measure body (where the rotor gets installed) will help with smooth operation. Don't get rid of the graphite - just the powder.
I have my Uniflow mounted on one of the newer RCBS stands. If there's a lot of powder still in it, I remove the measure from the stand and pour the powder out of the hopper. If there isn't much left, I just run it though the measure, one charge at a time. Either way, I give it a few solid flips of the charging handle, to dislodge anything stuck in the metering chamber (including while upside down, if pouring it out).
After that, it gets a good visual inspection to ensure it really is empty.
Every once in a while, I'll wipe down the outside of the hopper with a dryer sheet, to keep static down (dry climate).
"Such is the strange way that man works -- first he virtually destroys a species and then does everything in his power to restore it."