A Gascolator (fuel filter) acts primarily as a fuel drain and is usually found in the lower regions of an aircraft's fuel system. This allows it to drain any water that may have found its way into the fuel (some fuel is lost when draining).
A gascolator is usually made from a high quality alloy and is of a relatively low cost compared to other aircraft components. It should be installed at a low point in the fuel system, below the fuel tank to trap any water that may accumulate so it can be drained. The gascolator has a micrometre sized fuel filter and approximately a 3 mm pipe thread outlet for a quick fuel drain valve.