I found myself very bored one day and decided that I needed a water pack that I could take to school and not have to stuff a camelbak in my backpack, so I made this.

Improvements: One could find or make some device to seal off the hose when needed, sometimes it leaks when putting it on.

Step 1: Materials

Oops! Forgot to take a picture of the materials! Sorry!

You need:
1x 1/2" cross
2x 1/2" 90 degree elbows
1x 1/2" plug (an end cap would work also)
3x water bottles
about 3' of any size (less than 1/4") flexible tubing
a glue for plastic (shoe goo worked for me)
about 1' of 1/2" PVC
pipe cutters
any knife (box knives work well)
a power drill with a drill bit kit
PVC glue
a thin file
about 4' of thin rope, to tie the contraption to your back.

Step 2: Cutting the PVC

Cut 5 2" plugs of the 1/2" PVC. These will be used in connecting all the bottle caps, elbows, and the cross. If you bought an end cap instead of a plug, cut one more plug, to attach to the cap.

Now grind the rims of three of the plugs so that the edge is almost sharp. These will be the plugs that attach to the caps.

Sorry for the blurry photos...

Step 3: File a Notch in the Sharpened Plugs

Use your file to now create a notch in the three sharpened plugs. These need to be closer to the sharpened side of the PVC, so they won't be covered by the elbows and the cross. If you don't have a file this thin, you can use the side of a bastard file,this works also.

Notice that the notch is not too deep, because, if it is, you cannot achieve a full seal.

Step 4: Cut the Caps

Now you need to cut out the center of the three caps. You must make the cuts right inside the ring that fully seals the top off. Costco (Kirkland) water bottles work well, I don't know how other bottles would work out. It is very important to not leave any ridges along the inside, this cut must bea s smooth as possible.

Step 5: Attach the Caps and Notched Plugs

This is the weirdest step. You need to attach the caps and plugs with a few different types of materials. First, smear a generous amount of PVC glue on the notch. Even though the glue will not bond with the cap, it will swell the PVC enough to partially seal off the flow of water. After that, you must force the cap over the sharpened end until it reaches the notch. Make sure that the threaded end of the cap faces towards the sharp end.

Now you must apply the other glue to the top of the cap and the PVC. This is to make sure that 100 percent of the water is held in the bottles. Most glues don't bond well to the water bottle caps but Shoe Goo does.

If you want to, you can wait until later to put the glue on. You should wait to use thicker glues and glues that expand.

Things that don't work: Gorilla Glue, PVC glue, Wood Glue (no I didn't try that, don't discredit me), School Glue

Thing that did work: Shoe Goo

Others like epoxy might work, but Shoe Goo worked best for me, and it is cheap and multi-purpose

Step 6: Drill the Plug (or Cap)

Now take your drill and a bit that is one size smaller than your hose and drill a hole in the top of the plug. This allows you to feed the hose in with a perfect seal.

Step 7: Put It All Together!

Now attach everything together. Make sure to apply a generous amount of PVC glue to each element.

After that feed your hose down through the plug (or cap). It should come out of the bottom of the cross, through the plug and cap, and stick out far enough to touch the bottom of the water bottle on bottom.
(If you have trouble making the hose fit, you can cut the tip of the hose off to a point. This helps in two ways: the hose will never suck onto the bottom of the water bottle, and the hose is easier to put in)

If you waited to put glue on, now is the time. Smear or dab the glue into the slot between the cap and coupler, and let it dry.

Step 8: Paint It

As we all know, paint makes a project look much, much better. Choose any colors you want, and paint away. I highly recommend painting this, otherwise you get lots of strange comments from those around you.

When you paint it, make sure that you have three empty water bottles attached to it, so it doesn't get paint in any part that water touches, because I don't really fully trust paint chemicals.

Step 9: Construct a Back Strap

You can use any type of thin rope. Tie a slip knot (or a clove hitch or a two and a half hitches) on both ends of your rope, and then tie a pretzel knot with a loop around the top plug. Adjust to fit you.