It's not the answer you would probably like to hear, but double bagging (regular kitchen bags not double yellow bags) was a solution that we used for a long time.

When I was younger, I was, uh...inefficient when it came to the cat litter. I didn't scoop out the boxes, instead I fully changed the boxes every 3-4 days. I would pour it into a grocery bag, then out it in the kitchen trash (double bagged), and then take out the trash.

They always took the trash, despite being probably 10-20 pounds overweight.

Like I said, nice the idea system, but it does work.