Empty helium tanks can be recycled or disposed of in the trash. However, it is important to prepare the tank properly before recycling or disposing of it. Here are the steps to prepare an empty helium tank for recycling or disposal:

1. Wear protective gloves and goggles.
2. Tilt the black nozzle to release all helium until empty.
3. Unscrew the white valve nut and remove the nozzle.
4. Remove the disk on the tank.
5. Circle the open hole and write "empty" on the tank.
6. Take the tank to a recycling center or household hazardous waste department at the refuse center.
7. If the tank is less than 5 gallons, it can be safely disposed of in the trash. Make sure to turn the top valve to the left to release all the helium before putting it in the bin.
8. If the tank is greater than 5 gallons, take it to the household hazardous waste department at the refuse center.

It is important to note that improperly disposing of helium tanks can put waste workers in danger. Therefore, it is crucial to follow the proper steps for recycling or disposing of empty helium tanks.