Okay, here's my system.

Main tanks: Three 55-gal Greek pepper barrels and one 66-gal Pepsi concentrate barrel. My preflush is simply some 4" PVC that fills up first and then the following water flows into the Pepsi drum. I have to manually unscrew the plug at the end of this PVC tubing to drain the preflush. All these barrels are plumbed together so they fill at the same time. You can't see it in this picture but the rain water enters the barrel through a basket lined in mosquito netting. This fliter is easily removed for cleaning.

Rain1 by merriwether, on Flickr

Secondary 66-gal Pepsi concentrate barrels. These are hooked to side gutters on the house, though the first one handles a very large section of roof. I wish I had room for another there. Neither of these currently have preflush systems.

Rain2 by merriwether, on Flickr


Rain3 by merriwether, on Flickr

The barrels are all raised above the levels of the beds they serve so I can use gravity to deliver the water where I need it.

-Blast