our favorite vacuum pump oil
This is the same oil that will come pre-packaged with your freeze dryer, but they wont send much more than can be used to run one load. We bought this oil because it is sold by the same people who make the pump. Several users believe this oil helps the pump pull a vacuum as quick as any other oil.
You'll want to buy at least an extra gallon or two if you prefer to freeze your oil to remove water and then run all the oil through a toilet paper filter between loads. We have one freeze dryer, but we cycle three loads worth of oil. The pump will contain oil while we're freezing another pump's worth of oil and filtering another in the toilet paper filter. You don't have to it this way, but we believe it helps keep things efficient when we're trying to get the next load into the dryer.
Filtering your oil will allow you to re-use the same oil, which will allow this gallon to last months instead of weeks.