Some soils are difficult to clean from the pots in the Fritsch mill. They stick to the sides and create a thin layer or edge that can't be removed with water. Cleaning sand can be used to solve this. It consists out of sand with no organic matter, low iron content and pH neutral. Fill the pots with enough soil to cover the 10 balls and mill for 3 minutes. The sand will remove the soil particles from the pots and keep them clean. Use cleaning sand at least once a day to keep your pots clean. This can be repeated more often when working with extremely sticky soils.
Cleaning sand can be asked to get via SoilCares or buy it yourself. Take a bag of course masonry sand (silversand or washed sand) from the DIY shop and dry it fully. Store it in a plastic container to keep it dry. Be careful not to use beach sand this contains a high level of shell parts which can influence the pH measurement of your soils.