Abstract: A drainage system for draining fluid from a liquid storage tank and a method of draining a liquid storage tank using the drainage system, the drainage system comprising: a first conduit configured to fluidly connect to a liquid storage tank; a plurality of second conduits, each second conduit being fluidly connected to a measuring tank configured to hold liquid drained from the liquid storage tank; a multiway valve comprising: a first passage fluidly connected to the first conduit; a plurality of second passages, each second passage being fluidly connected to one of the plurality of second conduits; and a controllable shutter configured to selectively direct fluid between the first passage and the plurality of second passages; and a pump arranged to pump fluid through the first conduit.