This is the set up to produce stationary wave. The oscillator on the left will produce wave on water surface then this wave will travel to right, reflected at the tank and the incoming and reflected wave will superpose to form stationary wave.
My teacher said when the water wave hits the tank at the right side, antinode of stationary wave will be formed because it is a free end. I don't understand why it is a free end, I thought it as a fixed end since the tank is a rigid container. My analogy is at the closed end of a closed pipe, node is always formed, not antinode so why at the tank an antinode is formed?