Vacuum exhaust piping (from the pump to the point that it discharges) is permitted to be made of copper or stainless, but is it required to be installed using copper or stainless?  Is black iron, galvanized, or anything recommended by the manufacturer permitted?

5.1.3.7.7.6 -  Vacuum exhaust piping shall be permitted to be made of materials and use a joining technique as permitted under 5.1.10.2 and 5.1.10.3

5.1.10.2 -  Piping Materials for Field-Installed Medical-Surgical Vacuum and WAGD Systems

5.1.3.7.1.1 Medical–surgical vacuum sources shall consist of the following:

(5) Piping between the vacuum pump(s), discharge(s), receiver( s), and vacuum source shutoff valve in accordance with 5.1.10.2, except brass, galvanized, or black steel pipe, which is permitted to be used as recommended by the manufacturer

(6) Except as defined in 5.1.3.7.1.2(1) through (5), materials and devices used between the medical vacuum exhaust and the medical vacuum source that are permitted to be of any design or construction appropriate for the service as determined by the manufacturer 

Yes Clear As Mud Again.

NFPA 99 in my opinion only.

Is a field installation document.

The manufacture can use any material they like.

But the patient distribution and the exhaust or intake piping system .

Shall be per the book and each section it relates to.

 Agree with Al cannot see photo well enough.