I figured out it really helped to keep my used rolls of filament in vacuum bags with desiccant.

Got an inexpensive kit with 10 bags and a hand vacuum pump from Amazon. First time I used it, I had to get my wife to work the pump while I held everything in place because the back side of the bag kept closing off the vacuum valve. Really needed 4 hands: 2 to hold everything in place and keep the bag open where the vacuum valve goes through, and 2 to work the pump. Thought if I had a spacer I could just lay the bag flat on something hard and that would work to back up the pump, but let the air escape from the bag, it might work with just my hands. 

Created this little spacer in Openscad (file included). This version of the spacer is designed to work with the vacuum pump in the kit linked above. The Openscad file is parameterized so that if you need a different diameter or height, you can just change the parameter for that feature. It's pretty self explanatory once you look at the file.

Enjoy!