So your playing a water gun fight. Suddenly, in the midst of chaos, you run out of ammo. So you run to the faucet Then you get hit. Damn you say, so you resort to instructables and you see this. There you go. I will show you how to make a water gun with up to 6 liters capacity (if you can carry it!)
Kinda cool having it, plus you have the choice to modify the squirter.

Step 1: What You Need:

A small spray bottle (used in glass cleaners)
Bottle containing your liquid of choice and ;
Airline tubing used in aquariums

Step 2: Hole!!!!!

Make a hole in the cap of the bottle enough to fit the tubing and insert it. If you are a pretty active player, seal it off with hot glue or silicone or any non-water based glue.

Step 3: Cut and Insert.

Cut a small piece of the tube from the spray and insert it in. Make sure that the tube you cut has enough length so that you can insert the airline. Seal if you like.Replace the gasket if any.

Step 4: Attach, Prime and Go!

Attach everything together and repeatedly pump the spray until you get a continuous supply of water. Put inside a backpack and have the airline tubing and spray at your hand to have the S.W.A.T. look. Paint the pump using a sharpie or markers a black coat. Ready to fight!!!!

Step 5: Refilling

Refilling is easier than it looks like. Have a spare bottle in your bag and switch if you ran out. If your tubing is long, then you have some spare shots left in the tube.Start refilling if you can see air in the delivery tube.