Half of the bottle.

Remembering that the wizard said not to drink the whole bottle, you decide to play it safe and only drink a quarter of it. 'Wow it even tastes better than Coke or Pepsi' you think, and before you stop, half of the bottle is gone.

You feel yourself hardening. Soon, there's a noticeable bulge tenting your jeans, before you realize it's happening, you feel the pain of your dick reaching the limit of your jeans. Unbuttoning them and looking down, your mind is filled with both shock and amazement. Your cock is still growing and it's at least double your previous measurement. It doesn't stop getting bigger until it's about five times the length it used to get to, and at least 3 times as big around.

"Come on man hurry up!" you hear a feminine voice say, from where the brunette with the lips went into.

You look over at the glory hole you saw a moment ago.