In the flushing test, a liner's flushing resistance is tested under defined conditions. Flushing resistance is required because sewers are flushed regularly for cleaning and removal of obstructions. A hose with a flushing nozzle is pulled through the lined pipe. Dirt is flushed from the sewer with high-pressure water. In the past, the "Hamburg model flushing test" was used. In this test, the liner was subjected to 30 flush cycles from a flushing head with eight 2.6 mm nozzles and a water pressure of 120 bar. If the liner was undamaged afterwards, then the test had been passed. Since about 2 years ago, the test is conducted according to DIN 19523. This test can be done in the laboratory. Its principal difference from the Hamburg-model flushing test is that not the pressure but the jet energy density is the critical parameter. The liner is exposed to a jet energy density of 330 W/mm², which corresponds to a pressure of 90 bar at a flow of 280 l/minute. If the liner shows no signs of damage after 60 cycles, then the test has been passed and the liner can be installed. In addition to the Hamburg-model flushing test and the test according to DIN 19523, there are other national tests like the Quik flushing test in Switzerland. In addition to high pressure and numerous flushing cycles, this test also adds gravel to the flushing water to increase the abrasive effect.