For an exercism exercise I wanted to do multiplication with the pipe operator, and simply using * does not work, neither does (*).
Now, it turns out the arithmetic operations are functions part of the Kernel module, and you can also call them as an actual function with Kernel.*(2, 2), which is equal to writing 2 * 2.
This enables you do do arithmetic as part of the pipe operation, see:
def monthly_rate(hourly_rate, discount) do
hourly_rate
|> daily_rate
|> apply_discount(discount)
|> Kernel.*(22)
|> ceil()
end