Abstract: A tank interceptor for rain water and waste-water includes a container which has an intermediate partition dividing the chamber into a by-pass compartment above the partition and a treatment compartment below. An inlet is positioned adjacently above the partition and an outlet is also positioned adjacently above the partition, but spaced away from the inlet. The partition includes a raised portion isolating the inlet from the outlet, such that liquid entering through the inlet and seeking to reach the outlet through the by-pass compartment must overlow the raised portion in order to do so. Openings are provided through the partition on the inlet side and the outlet side of the raised portion, and communicate the by-pass compartment with the treatment compartment. The openings are such that liquid, without having to overflow the raised portion, can travel from the inlet to the outlet through the treatment compartment.