The Collaborative International Dictionary of English v.0.48:

Sewage \Sew"age\, n.
   1. The contents of a sewer or drain; refuse liquids or matter
      carried off by sewers
      [1913 Webster]

   2. Sewerage, 2.
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Sewerage \Sew"er*age\, n.
   1. The construction of a sewer or sewers.
      [1913 Webster]

   2. The system of sewers in a city, town, etc.; the general
      drainage of a city or town by means of sewers.
      [1913 Webster]

   3. The material collected in, and discharged by, sewers. [In
      this sense sewage is preferable and common.]
      [1913 Webster]

WordNet (r) 3.0 (2006):

sewage
    n 1: waste matter carried away in sewers or drains [syn:
         sewage, sewerage]

Moby Thesaurus II by Grady Ward, 1.0:

42 Moby Thesaurus words for "sewage":
   BM, bilge, bilgewater, bowel movement, buffalo chips, ca-ca,
   carrion, coprolite, coprolith, cow chips, cow flops, cow pats,
   crap, defecation, dingleberry, dishwater, ditchwater, droppings,
   dung, feces, feculence, garbage, guano, jakes, manure, movement,
   night soil, offal, offscourings, ordure, refuse, riffraff, scum,
   scurf, sewerage, shit, slop, slops, slough, stool, swill, turd