How to Make a Backpack Water Gun

Place the backpack on your work surface and open the main compartment. Locate the center of the bottom and cut a small hole in the fabric.

Center the fabric grommet on the hole and snap the two halves together, one on the outside of the backpack and one on the inside. You should have an opening in the bottom of the backpack that cannot be torn further because of the metal of the grommet.

Mark the center of the cap of the empty gallon jug and drill a 3/8-inch hole through the center of the cap. Remove the cap.

Push one end of the plastic tubing through the hole in the cap so there are 2 inches of tubing coming through on the end that will go inside the gallon jug. Seal the tubing to the cap using waterproof auto gasket sealer, and tape the tubing to the cap with duct tape.Make sure you do not obscure the threads on the inside of the cap.

Feed the end of your plastic tubing through the grommet in your backpack just enough to get it started.

Fill the jug with water and screw the cap on tightly. Turn the jug upside down and keeping the free end of the plastic tubing pinched shut to prevent water from flowing out, put the upside down jug into the backpack so the cap lines up with the grommet.

Remove the fill plug from your water gun and insert the free end of the plastic tubing into the fill-hole making sure their are no kinks in the tubing. Tape the tube to the body of the gun.

Pad the inside of the backpack with Styrofoam packing to keep your jug upright. Close the backpack.