hmmm I was going to ask a similar question and a few extra as well...
1 can two litter bottles from your fav soda pop be used?
2 how about bottles from juice IE the ones that are fairly square?
3 Would the quart and 2 quart containers available in paint departments of the large box stores work?
4 I posted an idea in the first S/H topic about putting window screen in to stop roots from going down into the water, (bad root no fertilizer), would that work or would it stop the wicking action or has anyone tried it or something similar?