The Testing tank is a laboratory for testing oceanographic instrumentation, which is used in measurement campaigns or fixed observation sites. It is also used for testing prototypes that are developed in the laboratories of the OGS Oceanography Section. 

It consists of two tanks, both equipped with a filtering system, a larger one (L-shaped; maximum length 9.9 m; maximum width 3.6 m; depth 1.4 m) filled with fresh water and a smaller one (2 m x 1.5 m x 0.9 m) filled with sea water. The latter is used in particular for balancing Slocum gliders before launching them. The laboratory is also equipped with a small bridge crane for handling the instruments with a load capacity of up to 200 kg.