The Collaborative International Dictionary of English v.0.48:

Ajutage \Aj"u*tage\, n. [F. ajutage, for ajoutage, fr. ajouter
   to add, LL. adjuxtare, fr. L. ad + juxta near to, nigh. Cf.
   Adjutage, Adjustage, Adjust.]
   A tube through which water is discharged; an efflux tube; as,
   the ajutage of a fountain.
   [1913 Webster]

Bouvier's Law Dictionary, Revised 6th Ed (1856):

AJUTAGE. A conical tube, used in drawing water through an aperture, by the
use of which the quantity of water drawn is much increased. When a privilege
to draw water from a canal through the forebay or tunnel by means of in
aperture has been granted, it is not lawful to add an adjutage, unless such
was the intention of the parties. 2 Whart. R. 477.