The Odyssey by Homer Book 10 Page 33

When your ship has traversed the waters of Oceanus, you will reach the fertile shore of Proserpine’s country with its groves of tall poplars and willows that shed their fruit untimely; here beach your ship upon the shore of Oceanus, and go straight on to the dark abode of Hades. You will find it near the place where the rivers Pyriphlegethon and Cocytus (which is a branch of the river Styx) flow into Acheron, and you will see a rock near it, just where the two roaring rivers run into one another.

“‘When you have reached this spot, as I now tell you, dig a trench a cubit or so in length, breadth, and depth, and pour into it as a drink-offering to all the dead, first, honey mixed with milk, then wine, and in the third place water — sprinkling white barley meal over the whole.