From the product description, check product page for current description, price and availability:

Not content with brewing just a single batch? The Double Batch is our bundle for you. Containing two of our FermTank – 8 gallon fermenters this gives you the capacity to ferment two 5.5 gallon batches.

So whether you have a party coming up, want to use different yeast, or just like have extra beer around the place, this bundle is for you!

Features:

• 16 gallon total capacity (2 8-gallon fermenters)
• Includes thermowell and ball valve
• Pressurizable to 5 PSI for pressure transferring
• Racking port with rotatable racking arm
• Has a 3/4″ welded drain valve for easy cleaning
• Height adjustable legs
• Gasketed lid with locking clamps for an air-tight fit
• Domed lid with hose barb blow off. Lid also has an extra port with plug & o-ring.
• Dimensions without lid: 24″ h (28″ w/ leg extensions), 13″ diameter, 8 gallon volume.
• Total height with lid and blow off barb: 28″ h (32″ w/ leg extensions)