Water proof electrical box

I installed a switched GFCI receptacle for a pool on a piece of 7/8 in x 10 ft strut driven 6 feet in the ground with the other 4 ft to mount the switch and receptacle boxes. I used to single gang boxes and a switch that looks like this http://www.grainger.com/Grainger/items/4YF69?cm_mmc=Google%20Base-_-Electrical%20Boxes-_-BELL-_-BELL%20Weatherproof%20Cover,%20Device%20Mounted%20Lever%20Switch%20Type,%20Number%20of%20Gangs%201,%20Ve
The boxes come with 1/2 inch openings in each end of the box and one in the back. It also comes with plugs.
I used 1/4 x 1 1/2 in bolts and 1/4 in x 1 1/4 washers to mount the boxes to the strut through the 1/2 knock out in the back of the box. I "ass"umed the washer inside, covering the hole, would make a seal tight enough to keep water out. I was wrong. After just a year the outlet failed.
It turned out that the top box with the switch was full of water to the level of the bottom lip of the box. It also was full of mildew.
Are the plugs that come with the box supposed to be water proof without using any sealer? Would it be a good idea to drill weep holes in the bottom of the boxes to let any water out? Does a washer in the back of the box make a water tight seal?
I plan on redoing the boxes and sealing the openings at the top and back, but is sure didn't seem necessary at the time.
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http://www.grainger.com/Grainger/items/4YF69?cm_mmc=Google%20Base-_-Electrical%20Boxes-_-BELL-_-BELL%20Weatherproof%20Cover,%20Device%20Mounted%20Lever%20Switch%20Type,%20Number%20of%20Gangs%201,%20Ve
That is exactly what happens if you don't use sealer on the threaded knockouts. Some bell boxes come with a small tube of sealent. I use clear silicone which works fine

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http://www.grainger.com/Grainger/items/4YF69?cm_mmc=Google%20Base-_-Electrical%20Boxes-_-BELL-_-BELL%20Weatherproof%20Cover,%20Device%20Mounted%20Lever%20Switch%20Type,%20Number%20of%20Gangs%201,%20Ve
Usually weatherproof boxes have small tabs that are attached on the outside of the box for mounting purposes, but they won't do much good for mounting on strut. Water is always a problem and I don't think that you can do enough to keep it out. Instead of using the knockout in the back for mounting, I would drill a hole or two through the back of the box just big enough for bolts to pass through. Put clear caulk around all of your knockout seals, bolts, and around the covers. Be sure to use an in-use cover for the receptacle.
A washer in the back does not make a watertight seal. I have heard of some people drilling weep holes in the bottom, but I don't know how well they work. I prefer to do as much as possible to keep water out. The 2008 code requires outdoor GFI receptacles to be weather resistant. They should have a "WR" on the face (Art. 406.8).
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wrote:

Anything used outside is considered a wet location and it usually is. Drill a small hole in the bottom of the bell box to let the water out. In outside boxes, always arrange the wirenuts to point up and put them toward the top of the box. (mitigates GFCI tripping) NFPA finally seems to be recognizing that water always gets in these boxes and they now require corrosion resistant construction in receptacles installed outside.
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