Potted plants need drainage holes at the bottom to release excess water, but you don't want soil to come out with it, especially if you keep your plant indoors. Luckily, all you need to keep it clean is a mesh bag (the kind you get oranges and onions in).
All you need to do is cut open a mesh plastic orange bag, fold it over once so it can trap more dirt, then set it across the drainage hole at the bottom of a new pot. Then, use some rocks to hold it in place, and add your soil and seeds. Water will run through the mesh as usual, but it will trap most loose soil and keep it off your floor
A New Use for Mesh Citrus Bags [Real Simple]