How to Make a Pull Pin Water Grenade

This is the paint/ water grenade I made. I took a segment of latex surgical tubing from a slingshot and tied a tight knot in one end and pumped water into the other end until it inflated like a balloon. I then took a bottle cap with a hole drilled in it and folded the uninflated part and stuffed it through. I slid a allen wrench through the hole preventing the cap from flying off until I throw it.