No doubt its inventors thought they'd make a fortune selling the disposable containers for it at $20 a dozen. Three cats can fill up a container every other day. There are people who can and will spend $20 every 24 days to get rid of kitty poop. I'm not one of them. Right away, I got the bright idea to line the containers with plastic grocery bags. That solved two problems: A single Littermaid container now lasted for 8-9 months and I can now do something with all those plastic grocery bags besides throw them out or hunt down some place to recycle them. I'd collect full grocery bags in one of those "flip top" trash cans and then lug the bucket out to the dumpster once a week. That worked pretty well. Changing the bags was easy, but I still had to change them every other day. And, let me tell you, three or four plastic grocery bags full of kitty "clumps" are astonishingly heavy.
Then one day while I was shopping in Wal-Mart, I saw those stackable drawer thingies they sell in a variety of sizes, and had a brain wave. I got one of the largest size they sell -- cost me $15, but turned out to be cheap at the price. I put a Littermaid container upside down and traced around it for the opening in the top of the drawer holder. I used my drill to drill a hole at the four corners so I could get a little hand-saw blade in and do the cutting. The drawer holder is not wide enough for all the Littermaid to fit on top so you have to put something beside it to support that end of the Littermaid. No problem. Whenever I buy something that is packed in big, fairly smooth pieces of solid Styrofoam I usually save them. They come in handy now and then when I need to "shim" things. Like now. The next thing I did was get a clean Littermaid container and cut the bottom out of it. 
It is important to note that there are some little notches on the bottom of the container that fit over two little bars on the Littermaid. When you are cutting the bottom off the container, DON'T cut these off! Cut around them. They are what hold the edge of the container against the side of the Littermaid. The bags I'm using are small garbage can liners -- they're pretty flimsy plastic so you might want to double bag. When you put the bag on, leave 4-5 inches of "cuff" to turn down over the sides of the container. On the side of the container where the notches are, tuck the edge of the bag over the bottom edge of the container and use some large paperclips to hold it. This will prevent the weight of the kitty poop from pulling the edge of the bag loose. Also, use a scissors to round the points off the corners on the top of the container so they won't poke through the plastic bag liners and tear them. Now you can put the container in the Littermaid in the usual way. I suppose you could put the container lid inside one of your plastic liner bags too before you affix it to the lid holder of the Littermaid. I don't, but you could. The lid does get kinda icky after a while.
It is important to note that there are some little notches on the bottom of the container that fit over two little bars on the Littermaid. When you are cutting the bottom off the container, DON'T cut these off! Cut around them. They are what hold the edge of the container against the side of the Littermaid. The bags I'm using are small garbage can liners -- they're pretty flimsy plastic so you might want to double bag. When you put the bag on, leave 4-5 inches of "cuff" to turn down over the sides of the container. On the side of the container where the notches are, tuck the edge of the bag over the bottom edge of the container and use some large paperclips to hold it. This will prevent the weight of the kitty poop from pulling the edge of the bag loose. Also, use a scissors to round the points off the corners on the top of the container so they won't poke through the plastic bag liners and tear them. Now you can put the container in the Littermaid in the usual way. I suppose you could put the container lid inside one of your plastic liner bags too before you affix it to the lid holder of the Littermaid. I don't, but you could. The lid does get kinda icky after a while. 
This is the finished setup. (I normally keep the drawer closed. It's open here to show the bottom of the bag hanging down.) Notice the large piece of Styrofoam next to the door jam (by my kitty's head) which is there to support that end of the Littermaid. I took this pix before I realized the importance of securing the edge of the plastic bag to the bottom edge of the container. If the paper clips were in place, you would be able to see them in this picture, or at least one of them.My kitties caught on right away. They can easily climb on the edge of the drawer holder to get to the Littermaid. But, if your kitties are older or do not handle change well, you may need to "walk them through" how they get to the poop box now. Some kitties resist change. Some are just stubborn. You might want to put plastic down on the floor around the new setup until they get the hang of it, or if you anticipate a contest of wills. If your kitties are older and have difficulty getting around, I suppose you could make them some stairs if you are handy with woodworking. I have a throw rug down under mine because I rent, and the utility room is floored with that nasty old cheap grey "asphalt tile" from the 1960's -- the kind you have to wax, and that was in every school I ever went to. It's ugly, scuffed, and icky.
When the bag is full, remove the paper clips and pull the top of the plastic bag loose from around the container and twist tie it. If you pull the plastic bag up on the side of the container you can easily get to and push it under the lid assembly far enough to where you can pull it through from the inside, it's much easier to get the bag loose from between the container and the Littermaid. Don't let the bag get real full the first time you change it. There is a learning curve involved here. I suppose you could wear a pair of old rubber dish washing gloves to do it, but I just use my bare hands and wash my hands good with antibacterial soap afterwards. Notice the little notches sticking out on the bottom of the Littermaid container. Those are what you don't want to cut off when you're cutting the bottom out of the container.
When you've twist tied the bag, reach in and flatten it down with your hand so you can get the drawer open. Also, open the drawer carefully so as not to tear the bag. If you didn't double bag, you might want to carefully roll it over into a plastic grocery bag before you try to move it just to reinforce the bag. I certainly would not want to have to clean up the mess that would happen if a bag tore.Now remove the container from the Littermaid and put a clean bag on, put the container back on, and you're ready to go.
This little modification will almost "fourple" the capacity of a Littermaid container. With three cats, I only have to change the bag every five or six days. Now that I have four, I change it about every four days.
Now that I've worked with this modification a while, I can suggest several improvements. The Littermaid containers are kind of flimsy. I tried gluing two together, one inside the other. This didn't work very well because the side of the container that goes up against the Littermaid had a tendency to bow inward and stuff falls through the gap. However, I tried it again with two more containers only this time I cut a piece out of the inside container on each side to decrease its diameter, which solved the bowing problem. You also need to choose your glue wisely -- choose the kind that says it glues plastic. Otherwise, the glue may melt the plastic. Also, I would put the hole in the drawer holder more in the center of the drawer. This would enable you to use a tall kitchen trash bag liner. Not only do they hold more, but the tall liners are made of more substantial plastic. I don't think I would have enough room to do this with my current setup, and there's no other place where I would want to put my Littermaid that is near a plug.
If you keep your Littermaid in the garage, where odor is less of a problem, you might want to consider doing it this way: Cut the hole in the drawer holder about half an inch smaller on all sides and put the hole in the middle rather than close to the edge. Then put a litter box liner in the drawer. You could use those really big, heavy duty paper clips that clip a bunch of papers together to hold the litter box liner onto the drawer. Then put a bag over your Littemaid container, but cut the bottom out of the bag so it will act like a chute and let the poop fall through into the lined drawer. When the drawer gets as full as you can deal with, open the drawer, take the liner loose, twist tie it and dispose of it. Reline the drawer, and you're back in business.
I've seen commercials for a new "automatic litter box" that flushes itself with special solution and "liquifies solid waste," dumps it all into the toilet bowl, then blow dries the litter. Nice idea. Certainly an improvement on the Littermaid, but you've still got to flush the toilet -- and buy the flushing solution stuff -- want to bet it's pricey? However, lets face it. Nothing will really solve the problem until somebody invents something porcelain that attaches to plumbing pipes, drains into the sewer, and flushes itself automatically. If they do the job right, it can be easily (and cheaply) modified to work for dogs as well as cats.
They could call it "The Pet Bidet."
P.S., I refer you to the post for Monday, December 08, 2008,
The Poop Box Modification Revisited, for the latest tweak. . .
