The spigot line should not come off the actual RO housing itself, but be a branch off of the tank line. Remove the tee that branches it, and run a single line into the garbage can for good water.
If you cannot remove the spigot line, then just get a valve to fit on the end to close it off, or yes, put it in the garbage can too. My unit had the same feature, as it was sold at a dept store for drinking water, not marketed to our sector.
I repeate, it is not neccessary to hook up the spigot line to anything other than a collection can if you cannot remove it.

Peace