Apparatus and method for filtering contaminated fluids at various locations using at least a first and second filter unit mounted on a mobile base. Each filter unit has a plurality of filter vessels with each of the filter vessels having a plurality of filter elements and dual plate mounting. In each filter unit, the contaminated fluid is first coarse filtered and then fine filtered. Means are provided to by-pass either the first or second filter unit so that the filter elements can be changed or for by-passing both the first and second unit when desired.