They vary by manufactuer.
What does the exterior portion look like?
Is it a surface mount with three screws?
Is it in a hatch?
There are different configuration. Some have a male pipe thread and some have a female. You almost need to take it out so as to get the correct one and probably a new pipe fitting to connect pipe to it.
You could look through this site for yours.
Water inlets
Bud
USAF Retired
Pace Arrow
2003 Chev Ice Road Tracker