The Hydraulic Telegraph

There's one from, not the oldest of greek history, but like maybe fourth century b c, greece, that is called a a hydraulic telegraph. What this guy developed were two great big brass buckets, right full of water. They're specked out identically and there's a spigot on the bottom. It has two positions, all open, all closed. Now what happens is, you use a torch, with both buckets with identical messages on opposite sides of the hill full,. You use a torch to signal open the pigot. You open the spigot, then you raise your torch to say, close it. If we can calculate how long