Last week my husband took a close look at my rain barrel and came up with semi self cleaning idea for it. The barrel is up on a stand and has a spigot that is as close to the bottom as he could put it. He attached a hose to the spigot and placed a clamp so that the hose end is held about two inches below the top of the barrel and left the hose end open. Now when it rains, if the barrel gets filled to overflowing, the overflow is coming from the older, stale water near the bottom as opposed to the fresh water coming into the top. Not perfect but i think it helps. The hose end is screened just as the input area is against bugs.