Slick does not mean the line has been primed
The name misleads people, and the wrong guess is a reasonable one. Nothing goes down a dry line on any pump. Before concrete, a wet slurry runs through and coats the inside wall so the load slides instead of grabbing, and that first material out the end never goes in anybody's forms. Hearing slick line, it is easy to assume the term describes a line that has had that done to it.
It does not. Priming happens whether the run is pipe, hose or both of them, and it is not a step anybody skips twice. Skipped, it costs far more time later than it ever saves at the start. The word slick is pointing at the pipe itself, at a smooth rigid bore that holds its own shape, rather than at anything done to the inside of it beforehand.
Worth keeping the two apart, because they turn up in the same breath on a pump site. One of them is a piece of equipment. The other is a step in every single pour.
Rigid pipe and flexible hose answer different halves of a run
Pipe holds its route once it is set. It does not kink and it does not get pulled sideways, which suits a long straight run that is going to stay exactly where somebody put it for the whole pour. Hose does the opposite job. It bends around a house, gets carried through a gate, and comes apart and goes back together when the forms move a few feet.
The place most people meet the word is around larger placing setups and around boom pumps, where concrete travels up a folding arm through pipe and gets placed from above. That is a different machine solving a clearance problem, and on the right tall or long-reach pour it is the right machine to hire. We do not own a boom pump.
What sits on our own trailer is a line pump running 2.5 inch and 3 inch line, with layouts built out of sections that clamp together on the site. Sections get added to reach around a house, and pulled back off when the forms turn out to be nearer than the plan allowed for. The work in this part of Virginia goes around, through and down into far more often than it goes up and over, and hose is the honest tool for that.
None of this is a ranking of equipment. It is a question about the direction the concrete has to travel and what is standing between the truck and the forms. Describe that trip in plain words and the machine, along with the kind of line hanging off it, more or less picks itself.