My first tri-strings were made with this design. It is simple and effective and can be adapted to materials on hand.
You can make great bubbles with super-simple tri-strings. All you need are two handles and some string or other wick material. This photo-essay shows a simple sturdy tri-string. In the pictures, I am using PVC pipe, but you could use just about anything. This tri-string was sized for a 4 year-old. This is a pretty good size even for bigger kids.
Click on the images to see them at a larger size.
Cut two pieces of string with the longer string cut to twice the length of the shorter string. The shorter string will be the top-string. I recommend about 21-24 inches for the top string and twice that length for the bottom string. Make the bottom string an inch or two longer than needed as some of the length will be used by the knots.
Tie the top-string (the shorter of the two long pieces) and the bottom-string to the leads. Wrap a piece of duct tape around the pipe handle to secure the lead. Decent duct tape is waterproof and will withstand much abuse.
You can also secure with waterproof glue (epoxy, super glue, etc) and use a fitting endcap for a more finished looking wand.