Let me be the first to admit this item is a bit hokey. It is clearly designed for moistening stamps, but it can also be re-purposed and used to activate veneer tape. It's cheap and it works. I started using one of these in my shop close to 20 years ago. It's been through the wringer, and it still works like a champ. 

Approximately 3" in diameter.

You can find these moisteners online for less, but I include a spacer ring made from an odd size of PVC pipe that fits inside and raises the sponge 5/16" above the top edge of the cup. This allows veneer tape to easily pass over the sponge and activate the tape with water. 

Two Tips from Joe

• Squeeze the polyurethane sponge under the faucet a few times to get it preloaded with water. Then place it in the plastic cup and fill it with water. To have the right amount of water in the cup, turn it upside-down and briefly press in the center of the sponge with your index finger. This will squeeze out some of the water. The remaining water will be close to the perfect amount for wetting veneer tape.
   
  
• Be sure to dry the sponge when you are finished using the moistener.