About the Altar
The altar is the very heart of the Holy Temple, for all of the Divine service is centered around it: all of the daily and additional offerings, as well as the individual and congregational offerings. All of the major ceremonies in the Temple also take place in the vicinity of the altar: the Passover offering, the bringing of the firstfruits on Shavuot, and even the rejoicing with the lulav branches on Sukkot all take place around the altar.

A Precise Location, From the Beginning of Time
The exact location of the altar is extremely precise, and has been established since time immemorial. The altar built by King David and King Solomon in the days of the First Temple, as well as the one built later in the era of the Second Temple, were both erected on the very same place: for this was the very place from which Adam, the first man, was created. The sages stated: "Man was created from the very spot which atones for him" (Bereshit Rabbah 14:6). Later, it was at this spot on Mount Moriah that Avraham bound Yitzchak upon the altar that he had built. Through that action, Avraham declared that this would be the place of G-d's Temple for all time.

Three Fires Atop the Altar
Three separate piles of wood burned atop the altar. The largest of these arrangements was designated to receive all the offerings; the second provided the coals for the incense altar within the sanctuary, and the third was the "perpetual fire" which constantly burned on the altar, as the verse states (Lev. 6:5) "And a fire shall burn there on the altar constantly; it shall not be extinguished." A large pile of ashes formed in the center of the altar from the remnants of these fires. G-d commanded that the coals be removed from here, and brought to another location outside of the Holy Temple which was known as the "place of ashes."

The Horns and the Ramp
The altar was built as a perfect square and was quite large: it reached a height of 10 amot (app. 5 meters) and its width was 32 amot (app. 16 meters). It was constructed of two main parts: the altar itself, and the ascent ramp. Both were constructed of stones and earth. On top of the altar at its four corners, there were hollow boxes which made small protrusions or "horns." These horns measured one amah square and 5 handbreadths high, each (or, app. 18" x 18" x 15"). The Torah states that the altar may not be approached by way of steps, since this would be considered unseemly and immodest behavior for this holy place: "Do not climb up to My altar with steps, so that your nakedness not be revealed on it"(Ex. 20:23).
The Service of Removing the Ashes
The service of removing the ashes is one of the positive commandments which relates to the outer altar. The Torah states:
"And HaShem spoke to Moshe, saying, command Aharon and his sons, saying: This is the law of the burnt offering: It is the burnt offering, which shall be burning upon the altar all night until the morning, and the fire of the altar shall be kept burning in it. And the kohen shall put on his linen garment, and he shall put linen pants upon his flesh, and take up the ashes which the fire has consumed with the burnt offering on the altar, and he shall put them beside the altar. And he shall put off his garments, and put on other garments, and carry the ashes outside the camp to a clean place... " (Lev. 6:3-4)
Following the dawn patrol, the officiating kohen who merited the task of removing the ashes now readies himself to fulfill this commandment. His fellow-kohanim warn him: "Be careful! Do not touch the vessel until after you have sanctified your hands and feet from the water of the laver!"

An Exhortation to Sanctity
They refer to the silver shovel which he will using especially for the purpose of removing the ashes. The actual intention of these words is that the kohen should remember that he must not begin his task until he has washed at the copper laver. In spite of the fact that he is already pure, and has even purified himself through immersion, one is still forbidden to begin any sacred Temple service (or even to draw near to the altar) until he "sanctified" his hands and feet at the laver. Thus the verses state (Ex. 30:20-21): "From there, Aharon and his sons shall wash their hands and feet; when they go into the Tent of Meeting, they shall wash with water so that they do not die; or when they come near to the altar to serve, to burn an offering made by fire to HaShem, so they shall wash their hands and their feet, so that they will not die. And it shall be a statute for ever to them, to him and to his seed throughout their generations."
Even though the kohen is certainly diligent and G-d-fearing, and well aware of the necessity for this sanctification without being told, it is still incumbent upon his brothers to warn him... for he goes to the altar alone, and as he is only human, he may forget this aspect of his duty. Once they have cautioned him, he stands forewarned.
At this time the other kohanim also remind him that the special shovel he will use for the ashes (one of the 93 vessels whose position was checked during the dawn patrol) is kept in the corner between the western side of ramp and the southern side of the altar. It will be there waiting for him.

Entering the Hall Alone
Thus heeded, the kohen is alone as he enters into the hall that leads into the Holy Temple's interior. No other man could accompany him, for entrance to the area between the hall and the altar or its ramp was forbidden to all but one who was engaged in performing the service. Since this particular aspect of the service was accomplished by only one kohen, he entered alone.
He carried no light, but made his way solely by the light of the fire which burned atop the altar. Thus he could not be seen by his colleagues once he entered the hall... for the other kohanim stood on the eastern side of the court, and this kohen now approached the laver which stood on the western side of the altar, to sanctify his hands and feet. Since the altar and ramp were quite high (10 amot - about 5 meters), it blocked all view of him.
This blackout in communications continued, between the priest of the first lottery and his fellows, until he reached the laver - and then, the others finally knew his position; not by sight, but by sound...

The "Muchni" of Ben Katin
What was it that the others kohanim heard? It was the "muchni of Ben Katin," the sound of a wooden wheel especially devised by one of the High Priests of the Second Temple by the name of Ben Katin. This mechanism was a large pulley shaped like a wheel by which the entire laver was lowered into a well at night, and pulled up in the morning filled with water.
"And you shall make a laver of copper, and its pedestal of copper... " (Ex. 30:18)
The laver, a large vessel which appears like a kettle, is actually the first vessel which the kohanim have contact with every day, for they must sanctify their hands and feet from its waters before commencing any sacred task in the Holy Temple.
The original laver which was constructed for the desert tabernacle in Moshe's time included 2 spigots for releasing the water. In the era of the Second Temple, the Kohen Gadol Ben Katin, who fashioned the muchni, also fashioned 12 faucets for the laver, so that the entire shift who participate in the offering of the daily offering may sanctify themselves at once.

The Laver Must Be Constructed of Copper
According to the verse above wherein G-d commanded Moshe to make the laver, it must be constructed of copper. Although many other Temple vessels were constructed of costlier metals such as gold or silver, thus giving greater honor to the will of G-d - the laver was to be made exclusively from copper. Even later, throughout all the subsequent generations of the Holy Temple, and even when the nation knew times of great prosperity and decorated the entire Second Temple in gold, the laver still remained of copper.
The Midrash (Bamidbar Rabbah 9:14) relates that the original laver was made from the contributions of the righteous women of Israel, who donated their shiny mirrors towards this cause. These mirrors, made of highly polished copper, were melted down and it was from these that the laver was created. This act of sacrifice was precious in the eyes of the Holy One - the fact that the women cared more about fulfilling the word of G-d than about their own appearance. He declared that the laver must be of copper throughout the ages, to invoke the merit of these righteous women, so the memory of their action will always be before Him.
The Reason for the "Muchni"
There is a specific concern of the laws of Biblical purity with regard to the copper laver, although the same problem can effect certain other vessels as well: anything left overnight in a sacred vessel becomes unfit for use in the morning. If water was left in the laver overnight, the kohanim would not be able to sanctify themselves with this water. Thus, the laver had to be emptied of its contents at the end of the day. But how could it be refilled quickly with enough water? In addition to this kohen who officiates at the removal of the ashes, all 12 kohanim who will soon be performing the daily morning offering must also wash their hands and feet at the laver!
Ben Katin, one of the High Priests who served during the era of the Second Temple, devised a system whereby this problem of ritual impurity can be circumvented: the mechanism of the muchni, meaning "machinery," or possibly derived from the word for "prepared." By emptying the laver of its contents from the previous day and then submerging in into a specially-made pool under the court, fresh water was obtained for the new day when the laver was hoisted up by the first kohen in the morning - he who goes to remove the altar ashes. It was this sound of the laver being raised up with the muchni that could be heard by the other kohanim in the court, on the other side of the altar.

"The Time Has Arrived!"
When the other kohanim heard the sound of the muchni raising the laver, they exclaimed "The time has arrived!" Meaning, the time of sanctification has come, for our colleague has now reached the laver. This was the signal for them to prepare themselves to begin their tasks, as well.