I leveled my 125 when full, it's funny how the tank could be level empty but when you add another 1000 lbs to the load it shifts. Many factors may apply, if you're tank sits on a concrete foundation then chances are it wont budge, but if you have a crawl space or on a second level the floor will give. I agree that you get it level empty and them ensure it stayed that way after it's full. if shims are required, use extreme caution when adding them, keep in mind the amount of weight that you are shifting around.