Let's assume you've built yourself a Figjam evaporative bucket cooler (for Burning Man, perhaps). It requires a certain amount of water in the bucket. If you let it run out, you run the risk of burning out the water pump. If you overfill the bucket, it reduces the surface area of the evap pad, reducing the cooler's effectiveness. So you need to constantly check and fill the cooler. If you are prone to want to use your cooler to take a long nap, as I like to do, that's a problem.

This Instructable will show you how to make a siphon feed for your cooler. After you set it up, it will keep your cooler at just the right water level by pulling from a 5-gal external reservoir. It doesn't need sensors, pumps, or any sort of electronics. Just simple physics.

I didn't consider I would be making an instructable while I was building this so you'll have to be happy with pictures of the already built (and playafied) product.

How it works:

There is a 5-gal jug of water up on a table The bucket cooler is on the ground. There are two tubes running from the carboy to the cooler, one carries water going from the water jug to the cooler, and the other carries air from the cooler to the water jug. The weight of the water in the water line is constantly trying to pull more water into the cooler (that's called a siphon). But the water leaving the water jug needs to be replaced by air. The water jug is a sealed container, so air can only come from the air line. The opening at the other end of the air line is at the top of the water level in the cooler, so is sealed by the water. This air seal prevents water from being siphoned into the bucket. When the water level goes down from running the cooler, the end of the air line is exposed, letting air into the water jug, thus letting water into the cooler, thus raising the water level until it seals the air line again.

What you need:

- Bucket cooler

- strange carboy cap (find at a homebrew supply store, or maybe online).

- 6-7' of small vinyl tubing (use the carboy cap for appropriate sizing).

- 5-6' of large vinyl tubing (again, use the carboy cap to size).

- 7" or so of brass or copper tubing, or other non-rusting, rigid, straight, skinny thing. I happened to use brass tubing because that's what I had.

- hose clamp, big enough to fit around the neck of the carboy.

- chunk of 1.5"-2" PVC pipe, slightly taller than the bucket. You want the interior diameter to be just big enough to accommodate the bundle of large tubing, small tubing, and brass tubing.

- piece of non-rusting hardware for weight, small enough to fit inside the carboy.

- plastic tubing clamp to stop the water flow.

Step 1: Bucket Inlet

This doesn't have to be the first step, but it's a step, and I'm writing it first, so it's the first step.

You need to make sure the hose stays straight up and down, and can slide in and out of the cooler without getting caught up on the foam pad. That's why I put a chunk of PVC pipe into the cooler.

Drill some small holes in the side of the bucket so you can pass some zip-ties through to secure the pipe.

Use a hole-saw to cut a hole out of the lid of the bucket just big enough for the PVC pipe, right at the edge where the pipe is going to come through.

Step 2: Bucket Insert

This is the part that goes into the pipe in the cooler.

Bundle and tape (or heat shrink) together the ends of the large, small and brass tubing. The distance from the end of the large tubing and the end of the rigid tubing will be approximately how deep the water is in the cooler, which should be just enough to cover the water pump, or it's inlet.

I believe I put the brass tube in the end of the small vinyl tube, so the water comes out the brass. That's not necessary though, you could run the vinyl all the way down next to the rigid tube and just past the air tube.

Step 3: Reservoir Attachment

This is the crux of the project. The 5-gal jug needs to be very airtight with all the tubes going in and out, and this hard-to-find cap is exactly what made that possible. I found it in a homebrew shop for $3. Maybe you can try looking online.

Whether you do this step first or the previous one, make sure when you cut the tubes, they are long enough for them to go from the top of the jug on a table to the bottom of the cooler on the ground. A little excess is okay, but you don't want it drooping to the floor.

Tape or zip tie the two lengths of tube together. Thread on the plastic tube clamp onto the water line before passing it through the cap.

The cap has two holes (large and small). The air line needs to go where the air is. It can terminate at the large cap hole. The water line needs to be where the water is, obviously, at the bottom. Pass it through the small cap hole and weigh it down with a piece of non-rusting hardware. I used a stainless steel eye-bolt.

The two vinyl tubes should be sizes such that they create a nice airtight seal when you attach one to- and pass the other through the cap.

To make sure there is a super airtight seal between the cap and the jug, I used a hose clamp around the cap. I also sliced up a spare chunk of the large vinyl tubing and put it between the clamp and the cap to protect from sharp edges.

Step 4: Use It!

The photo was obviously not taken with the intent to show off the cooler, but you can get the idea.

When you're ready to use your cooler, fill the jug all the way up with water. Put the cap on and clamp it down. Prime the water line (small vinyl) by sucking on it, or otherwise filling it with water. Then just stick the end into the cooler. The cooler will fill with water until it reaches the air line. It should bubble a bit and fill a little higher than the air line and then stop. When you're running the cooler, you will hear it bubbling every now and then. That means it's working! I would usually set the plastic tube clamp whenever I wasn't using the cooler, just in case. If there is a breach in the air seal, it would otherwise mean leaking water all over the place. Just don't forget to unset it, or it will mean burning out your water pump.