Mark drill hole guides on scrap piece of wood spacing them 1-inch apart.
Drill holes in base of one bin using 1/4-inch drill bit. To avoid cracking bin, press bottom of bin against wood below as you drill or use a step-down drill bit. TIP: Using the drill in reverse as you gently press down can reduce the chance of cracking the bin.
Stack bin with holes on top of the second bin.
Add a few inches of pine pellets.
Remove solid waste with scoop. Push sawdust through holes to bottom bin and clean out as needed.
Notes
Be sure to use bins with side handles which create a gap between bins when stacked allowing room for wet pellets (sawdust) to fall. Check local requirements for disposing of pet waste. For the best deal on wood pellets, check for wood stove pellets or horse stall pellets and check that there are no added ingredients. The same product marketed to cat owners can be double the price.