I've wanted for some time to install a slop sink in my utility room. I notice that about 16" to the left of the washer standpipe there is a 2" capped black plastic pipe sticking about 3" out from the wall. This pipe is 21" above the floor. I was hoping that this is a waste line the builder put there just for the future installation of a utility sink. Is this possible or might this pipe have some other use?