Any pictures would be helpful? Sorry, dog owner here ;)

I decorated one to use as storage. Hope theis helps. http://www.hometalk.com/9174773/repurposed-plastic-container-to-diy-pool-storage

DIY Pool Storage

pictures and/or dimensions would help. IDK what shape or size or material the litter containers you are talking about are.

If they are the square bucket type, you might be able to stack them on their sides and use them like bins.

I created a recirculating fountain with mine!

I must admit that I have no idea about the shape or size of these bins. If you were to stack them on top of each other, the difficulty would be in getting to the bottom one. You could separate them using shelves. There was a really great post on Hometalk sometime ago where the person made shelves using pipes, here is a link: http://www.hometalk.com/2964179/how-to-build-industrial-shelves

How to Build Industrial Shelves

More ideas here:

https://www.diys.com/repurpose-kitty-litter-containers/

I would build a rack that they can slide into. However, under bed storage seems like a good location. Label the outside so you don't need to open the top. You can always store Christmas or other holiday decorations in these boxes and place them on a shelf in the garage or other location.

Hi Sally, hope this helps you out,

https://www.diys.com/repurpose-kitty-litter-containers/

http://petslady.com/article/20-clever-ideas-recycling-kitty-litter-containers