what about a pond basket? You could further filter by affixing cotton muslin to the outside, or some other clean material--even cheesecloth--that would allow water in but not break down in a season. Contrary to popular belief, even in the best compost pile, cotton doesn't disintegrate in a year.

The first thing that comes to mind stems from my days of running aquariums. Some of the longest lasting and abundant filter material is polyester quilt batting. It is cheap, approximately $10 to $15 dollars and can be found at most craft suppliers. I found some at Wal-mart in their craft section. It comes in a roll, can be cut and you can easily cut it to fit your application, wrap something around your tubing to secure it (I am thinking rubber band or something easily removed) and can be taken out to rinse off or throw it away and cut another piece. You can experiment with how tight you wrap as this may affect the flow rate, I am just guessing here.

Thanks for the idea of a filter, I hadn't thought about that, but I will be putting a filter using the method described above, because if I know one thing about water storage, it always grows something "yuck."

Good luck, and if you found out another something that worked for you please get back to us.