The Collaborative International Dictionary of English v.0.48:

Excretory \Ex*cre"to*ry\, a. [Cf. F. excr['e]toire.]
   Having the quality of excreting, or throwing off
   excrementitious matter.
   [1913 Webster]

WordNet (r) 3.0 (2006):

excretory
    adj 1: of or relating to the process of excretion

Moby Thesaurus II by Grady Ward, 1.0:

33 Moby Thesaurus words for "excretory":
   egestive, eliminative, excretionary, excretive, exudative,
   lachrymal, lachrymose, lacrimatory, lactational, lacteal, lacteous,
   leaky, oozy, percolative, permeable, pervious, porous, rheumy,
   runny, salivant, salivary, salivous, secretional, secretive,
   secretory, seminal, serous, sialagogic, spermatic, transudative,
   watering, watery, weepy