A good tip when filling a stand column with sand or litter is to pour it into a bin liner within the column and tie a not in the top because most of the "kiln dried" sand I have come across is more often than not damp and laced with salt which rusts/corrodes away the metal over time. Cat litter too absorbs moisture and clumps together, so a good tight knot in the top of the liner prevents that and makes removal later a doddle.