Have empty CO2 cylinders, but no box? Want to join the Drinkmate CO2 exchange program? Get a specially designed Drinkmate CO2 Exchange box mailed to your doorstep. Send back 2, 3, or even 4 empty cylinders! Free Shipping! We will include a prepaid return label and instructions in the box. We accept Sodastream and Sodasense threaded 60L cylinders in our exchange program!No sign-up required! At Drinkmate we give YOU the option of how many empty cylinders you'd like to send back, or how many filled cylinders you'd like to order. Plus- the more CO2 you order, the more you save! More information on Drinkmate's CO2 Exchange program can be found here. *Includes the return box and return label only, no CO2 cylinders are included! All orders placed on idrinkproducts.com with more than one CO2 cylinder will automatically include a return box. There is no need to purchase one additionally.*Contact CO2@idrinkproducts.com if you have any questions. Cheers!