However, their habits can change, and in Citrus' case, it was an early sign that he was sick. He started pooping all over one of his imitation rocks. I would scrape off feces and clean it with dish-washing detergent (and a sponge reserved for that purpose). It didn't stop Citrus' rock from being so filthy that I eventually had to throw it out. Then, Citrus struggled to find a good spot. By then, I knew that it was especially important to keep his parasite-infected excrement as far away from him and for as short a period of time as possible. Unfortunately, he began to pick a spot right behind his home-rock, which was decidedly unsanitary. That's when I came up with the idea of a gecko port-a-potty!

Citrus loves it. From the very beginning, he's been using it as I hoped he would. The advantages are obvious:
1) It's easy to clean. Just fold up the used bit of towel and replace.
2) It's cheap. Instead of replacing all the towel lining the bottom of the tank (in this case, two sheets and a bit), you're only replacing half a sheet at a time.
3) It's easy to make and replace. It takes me five minutes and I replace it about once a month, as soon as the materials become available.

Materials:
Kleenex box
Paper towel
Cardboard
X-acto knife
scissors
Scotch tape

Step 1: Tear out the plastic lining the opening of your kleenex box and decide which way it will lie in the tank. Make sure you keep this orientation in mind at all times. Cut out more of an opening with the scissors for easy reptilian access.
Tip: The smaller, square boxes of kleenex fit into the tank perfectly. Some may be too big.

Step 2: Using the X-acto knife, cut along the top edge of your box to create a lid that will facilitate your clean-up.

Step 3: Line the bottom of the potty first with cardboard. The cardboard isn't necessary, but it reinforces the bottom of the box. Then line with two half sheets of paper towels.
Tip: Measurements for the lining should be approximate. Gauge where you should cut by approximating against the box. You'd be surprised at how tight a fit you can still get!

Step 4: Finish off the box with two pieces of tape to hold the lid lightly closed. I prefer to curl one end of the tape so that I can lift it off and open the lid more easily.

Step 5 (optional): If your gecko likes some privacy when going to the bathroom (who wouldn't!), it's a good idea to make a flap because the opening of the kleenex box is big. I cut out a piece of cardboard that is the same width as the potty and short enough that my gecko can still climb into the potty. I tape this flap, gray-side facing out, to the inside of the box for aesthetic purposes.
Tip: Keep your materials simple. My source of cardboard is any box I have at hand, for example, pasta boxes, and I use the same one to line the potty and make a flap.