Finally after many years of saying we should get eavestroughing we bit the bullet and called "the man" to come and get us all outfitted.  In our many years of procrastinating it had become clear to us that when we did finally get our act together we would want to have rain barrels to help buffer the flow of water coming out of the system.  The theory with rain barrels is that by storing some of the water that would otherwise be trying to get into your nice dry basement and releasing it later you can both save money on water to water your plants and help keep your basement dry.  Win, win all around.  Right only problem is that for $100 to $200 per barrel (and we wanted four) it adds quite the cost to the project.  Also most of the barrels out there are ugly or flimsy or both.  So when we found out recently that you could get used barrels that look just like some of the better rain barrels they sell for dirt cheap we immediately jumped at the idea.  Apparently they transport olives in 55 gallon (~210 liter) food grade barrels with nice screw on lids.  Aside from a few stray olives and a bit of brine in the bottom they were quite clean and seem to be quite strong.

We came up with a basic design and parts list based on observations of other barrels.  The design involves a hole in the top for the water to enter the barrel with a two layer screen to keep debris, mosquitos, animals, kids, etc... out.  The fine mesh keeps the mosquitos and small debris out while the heavy screen underneath ensures that a squirrel / kid doesn't go right through the fine screen.  Add a spigot 6" or so from the bottom and an overflow hose near the top and that's it.

Parts list:

Used olive barrel $15.00

Solid brass spigot $20.00 (this is a big of splurge but won't ever break like the cheap plastic ones)

Sump pump hose kit $8.00

ABS fitting to attach sump pump hose with $3

Fine fiberglass mesh window screen $10 (enough for 4 barrels)

Heavy galvanized 1/2" mesh garden screen $10 (enough for 4 barrels)

Other items we used:

6 Nuts and bolts

6 Washers

Heavy duty metal snips

Drill

Screwdriver

1/8" twist drill bit

1" spade drill bit

1 3/4" hole saw

The assembly process was pretty straight forward.  We started by giving the barrels a quick rinse.  While they dried out we brought the lids inside and drilled holes about 3/4" in from the inside edge evenly spaced around the lid.  (Note that the barrels seemed to come in two varieties: one with a one piece lid and the other with a two piece lid.  The two piece design is much simpler in that you don't need to cut a hole in the lid.)  We then cut out the heavy and fine screens to match the size of the lid.  The mesh is attached by holding in place (fine mesh on top, heavy on the bottom) and pushing the screws through the hole, and popping a washer and a nut on and tightening them up until snug.

We then drilled a 1" hole for the spigot 6" up from the bottom and a 1 3/4" hole about 6" down from the top for the overflow hose.  The spigot just screws in and has a washer and nut that secure it from the inside.  Having really long arms helps for this.  Otherwise you might have to lay the barrel on its side and crawl in.  The overflow assembly just screws on the same way but thankfully right near the top.  We've seen designs that have the overflow at the bottom and use a tube inside the barrel to prevent the water from draining until it reaches the desired level.  This sounded more leak prone and wouldn't work as easily to link multiple barrels for additional capacity.  The sump hose then just attaches to the overflow assembly and lets you direct the water far away from your foundation when (not if) the barrel gets full.  We ran a quick test (as it was already freezing at night) and found that a single barrel filled overnight with moderately heavy rainfall.