I've been after the plumbers to install the gas (propane) piping. At other of the builder's houses, I've seen this left until AFTER the owners moved in, and I wanted the dryer and cooktop to be available immediately. Gas pipe always used to be so-called "black iron" pipe, a sparkless variant of regular pipe. Cutting, threading, and fitting black pipe is a real pain in the butt, so I've been impressed with the use of this flexible piping. It's a stiff but flexible metal tube sheathed in a tough rubber-hose jacket.