(1) This subchapter applies to the following:

(a) pollutants from non-domestic sources covered by pretreatment standards which are indirectly discharged, transported by truck or rail, or otherwise introduced into POTW's;

(b) POTW's which receive wastewater from sources subject to national pretreatment standards; and

(c) any new or existing source subject to national pretreatment standards.

(2) National pretreatment standards do not apply to sources which discharge to a sewer which is not connected to a POTW.