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
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
any knife (box knives work well)
a power drill with a drill bit kit
a thin file
about 4' of thin rope, to tie the contraption to your back.
Step 2: Cutting the PVC
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
Notice that the notch is not too deep, because, if it is, you cannot achieve a full seal.
Step 4: Cut the Caps
Step 5: Attach the Caps and Notched Plugs
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)
Step 7: Put It All Together!
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
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.