How often you use the toilet and what size liquid container your model has will determine how often it needs to be emptied. Our liquid container holds 2.2 gallons. With the 2 of us using it full-time, we empty it every 3-4 days.  Once the handle on the solids tank becomes more difficult to turn, it’s time to empty it. For us, this is about once a month. The manufacturer recommends emptying it after 60-80 uses. We think not adding toilet paper to the pot helps extend this a little. If you don’t live in your van full-time or use the composting toilet infrequently, you can leave the solid tank for months because the waste will continue to break down.