A.P. van den Berg's Vacuum Device in order to obtain an excellent pore water measurement 

In addition to the cone resistance and the local friction, a Piezocone is able to measure the pore water pressure of the soil. In order to obtain an excellent pore water measurement, the space between the pressure sensor inside the cone and the outside of the filter, including the filter itself, has to be fully deaerated and filled with silicone oil. A.P. van den Berg's Vacuum Device is recommended for this operation.