Key objectives are:
-Use stuff lying around the house
-Don't spend ages getting it working
-Make sure everything get a good soaking.
-Keep and eye on environmental considerations
-Be Safe - Don't mix water and electricity!
Step 1: The pump and reservoir
The ideal reservoir would be a large bucket, but I didn't have one lying around that I could cut a hole in. Instead I had a whole bunch or plastic plant pots that could hold about one and a half litres. These are easy to cut and disposable (or at least their primary use is not affected) if I got it wrong the first time. Their problem is that they have large drainage holes cut in the bottom, which makes them less than ideal for holding water. A simple watertight fix for this is to put a plastic carrier bag inside the plant pot and force the input pipe of pump through a small hole in the bag. As the plastic is a bit elastic it helps to make a water tight seal. The pump has a rubber grommet which goes over the input pipe to create another water seal between the inside and outside of the container. Filling the reservoir with water and placing it on a dry surface shows me that it is not leaking.