Fermonster PET Carboy 6 Gallon Includes Lid with Hole Brilliantly clear with built-in 5-Gallon and 6-Gallon markers on the side for your convenience. Note: FerMonster XL has a built-in 7 gallon marker. The 4" wide mouth opening and rib-less side make mixing and cleaning a breeze. **Requires a #10 stopper or medium bung**