Libations
Libations, the outpouring of liquid in sacrifice to the gods, is one of the most common sacred acts in hellenic polytheism. Libations were so common in every day life that they were often offered whenever wine was drunk, at every meal, and at symposia and dinner-parties. At symposia specifically there was an established order for libations - to Zeus Olympia and the Olympian gods, to the heroes, and to Zeus again (commonly Soter or Teleios, or Agathos Daimon). [1]
[...] Heralds at once poured water over their hands, and the young men filled the mixing-bowls to the brim with wine and went round the whole company, pouring some into each cup for a libation to [Zeus]. When they had poured their libations and drunk as much as they wished, the envoys set out [...] Iliad 9.170-80
A libation is an offering and a sacrifice of wastefulness - what is spilled onto the earth cannot be brought back. The most common libations are:
wine
water
oil
honey
In the Odyssey 10.518-26, Odysseus pours three libations when beseeching the dead - one of honey and milk, then wine, then water.
There were two ways to make libations, depending on who the offering is for:
sponde - ouranic, made from a hand-held jug or bowl and a controlled partial pour (often shared)
choe - khthonic, a larger vessel held or which stands on the ground, poured out in its entirety
While the choe is specifically khthonic, the sponde is common and easy to offer, and could be performed at any time - this is a distinction which can be up to the individual worshipper.
To simulate the outpouring of a libation onto the earth during an indoor ritual, pouring the libation from a cup into a dish or bowl would easily suffice. The offering could then later be poured outside or disposed of in another fitting matter. (Please be considerate when pouring libations outside.)
Interestingly, the word spondai also means armistice or peace treaty. Interesting, because war is blood spilled - a libation of sorts, too.
[1] Burkert, Greek Religion pg 70-72 and Kearns, Ancient Greek Religion pg 92
