Howdy,RPM.
Let your imagination be your guide.
If you are using herbs or something like jerk paste,you may have to run your injectible thru the blender or strain through a fine wire mesh.
Remember the syringe has pretty small holes and cold meat provides resistance.
If you are injecting for flavor,use a chicken type rub mixed with a little beer,wine,stock,apple juice,etc.
For moisture,melted butter,oil,and a liquid of choice to make it flow through the needle.
You could just pump about 1 cup of Smokin's honey brine into each yardbird.
A good Italian salad dressing,run through the blender ,is a pretty good place to start.
Hope this helps some.