What size outlet valve does this IBC tank have?

It has a 2-inch (50mm) butterfly valve with an S60x6 male thread. Most garden and hose fittings won’t screw straight on, so you can add an adaptor at checkout. Depending on need, we would recommend the Hozelock, which is our most popular addition, or the 2-inch BSP female, 1-inch BSP swivel or Camlock. You can also add an IBC tap for easy filling of fans and watering cans. At the top, there is a 150mm (6-inch) screw cap for filling.