There is no such thing as cleaning your tanks too often. You should rinse your sap storage tanks off every day. Then, scrub the tanks every third day. Sometimes, you may need to scrub tanks every day if you're seeing a lot of film left over from the sap. 

By rinsing your tanks every day and scrubbing frequently, you will keep bacteria from growing, and your filtration, boiling, and RO (Reverse Osmosis) processes will go better. Regular tank cleaning makes your whole sugaring operation run more smoothly.