Knock out vessels are used to slow down gasses and allow liquids to "fall out" of the gas stream. Knock out drums can be installed either in the waste gas header, or in the flare stack base itself. Knock out drums can be configured in either a horizontal, or vertical arrangement. When horizontal, a knock out drum will be constructed with one gas stream inlet, and two outlets, which can then be joined with a manifold. Another configuration that can be used is one inlet with a much larger outlet. A liquid level gauge or indicator should always be included, as these vessels must remain drained and free of excess liquid. In a vertical arrangement the knock out drum can have a side inlet with a larger exit which will slow down the gasses