For replacing those gray hoses, I use clear vacuum tubing of the
type used for automatic milkers.  I can buy it from almost any good
hardware store or fleet supply house.

Unfortunately, it doesn't have the same eye appeal as an old gray
hose, but it's not a radiator hose and it doesn't suck flat either.
It maintains it's shape and can be stretched over the hose nipple by
immersing it in hot water.

I realize it doesn't come under the heading of "original" materials
for a restoration, but I've had no problems with it, or with customers.
They want the piano to work properly, they haven't cared too much about
the color of the hose.

The only other means of using the gray hose is to insert an inner coil
spring to prevent it's tendency to suck flat in use.

Musically,

Dan Armstrong
Armstrong Piano Tuning & Repair
Pine River, MN