Step 1: Materials
1x "T" connector (1")
Step 2: Construction
If you wanted to add more weight to it, you could fill it with metal pellets or something and cement end caps onto the pipes.
Step 3: Finishing
The result is a very lightweight practice tonfa. I tested it against a punching bag and it held up quite well. I'm not sure how effective it would actually be in combat, since it lacks weight.
For more information on how to wield and use a tonfa:
*Note: This is a weapon and can be dangerous if not used properly. I assume no responsiblity or liability for any injuries you or others sustain from the use of this instructable.