Abstract: The impermeability of a test piece, e.g., a pipe made of concrete, clay, stoneware, etc., is tested using a vacuum. Air in a compensation tank is maintained at a vacuum and also at a temperature that corresponds to the temperature of the inside wall of the test piece. Then, the test piece, sealed on both ends, has a vacuum generated therein that corresponds to the vacuum inside the compensation tank. Subsequently, the air inside the test piece is replaced with the temperature-controlled air from inside the compensation tank, and then the vacuum inside the test piece is adjusted to a predetermined testing level. The progression of the vacuum over a time period in the test piece is monitored. If the measured vacuum drops below a prescribed tolerance limit, the pipe is considered too leaky.