The intricate physical mechanisms involved during sloshing impacts in LNG tanks lead to biases in sloshing model tests when the impact loads are predicted. In order to increase the understanding of these biases, a new state-of-the-art facility dubbed the Multiphase Wave Lab (MWL) has been established. In the MWL, impact tests are performed within an autoclave (15 m long x 2.5 m diameter), whose purpose is to provide an accurately controlled environment in which the pressure, temperature and gas composition can be controlled and monitored. Wave impact tests are performed by generating waves in a flume which is located inside the autoclave. In this paper, we present the capabilities of the MWL to control the temperature, ullage pressure and gas composition in the autoclave. We study also the quality of the global flow repeatability by means of a breaking wave which is created with a wave-focusing technique. We quantify the repeatability of the waves with a Sobolevnorm-like criterion on the frequency domain and evaluate the repeatability for different ullage pressures. Preliminary experiments show a good degree of repeatability, in accordance with high-speed recordings of the impacting waves.