Nyal Williams wrote:
Our club has always used the standard hand signals
to let the tow pilot know the rope is taut and the
tow can begin.

We are considering short-handed operations in the early
hours of the day and will have just a wing runner.
Is there a standardized phrase or a recommended best
phrase to radio the tow pilot to begin the launch?
We need something that is specific for the tow pilot,
short, unambiguous, and easily understood.

Please don't say 'Go, Go, Go!' It violates almost
all the requirements.

We use: "Towplane X, Glider Y ready for takeoff (with/without water
ballast)"