“Six times a day we come out of the pool to drink blood. If we refuse…frightening demons come and torture us with metal rods before being thrown back into the blood pool. In the blood pool, countless insect like creatures with metal snouts come to pierce our skin and worm into our flesh to suck our blood.” [From Duncan Williams’ “The Other Side of Zen”]
The Ketsubonkyø, or the Blood-bowl Sutra, is a sutra composed in China around the end of the 12th century or the beginning of the 13th.4 It describes how Mokuren(Mu-lien, Maudgalyåyana), disciple of the Buddha famous for his supernatural or magical powers, descended to hell to save his mother. This narrative differs from the classic Mokuren story, as told in the Yü-lan p’en ching (Urabonkyø), which we explored in Chapter Three. In that story as it appears in the Buddhist cannon, Mokuren saves his mother from the realm of hungry ghosts. Here, however, we find her sunk in hell submerged in an enormous pond, or lake, of menstrual and birth blood. She is in the company of a multitude of women there who suffer abuse at the hands of the hell wardens and are forced to drink the blood. They are punished like this, the sutra explains, because the blood produced by their bodies spills on the ground and offends the earth gods, or ends up in rivers from which the water to make tea for holy men is drawn. This hell, called chi no ike jigoku (blood pool hell) in Japanese, threatens damnation for the sin of female biology. (It is worth noting that late medieval Japanese visual representations illustrate another hell for women who are unable to bearchildren, the umazume jigoku). [from Childbirth, Violence and the Mother’s Body by Hank Glassman]
Bussetsu Mokuren shokyo ketsubon kyo
[from “Menstration Sutra Belief in Japan” Takemi Momoka
Japanese Journal of Religious Studies 10/2-3 1983]Once the Buddha took 1250 biksus into the middle of the Deer Park. At that time, the venerable Mokuren put the following question to the Buddha: Once I went to such-and-such a prefecture, and saw in the middle of a large field there a Hell composed of a pond of menstruation blood. This pond was some 84,000 jujana wide, and in the middle women who were wearing handcuffs and ankle chains were undergoing hardships. The demon who was the lord of this Hell came here three times a day and forced the women sinners to drink the polluted blood; if they refused to do so, he would beat them with an iron rod. Their screams of anguish could be heard from great distances away. The sight of this made me very sad, and so I asked the Lord of the Hell why the women were being forced to undergo such hardships. He replied that the blood the women had shed during the birth of their children had polluted the deity of the earth and that, furthermore, when they washed their polluted garments in the river, that water was gathered up by a number of virtuous men and woman and used to make tea to serve to holy men. Because of these acts of uncleanliness, the women were now forced to undergo sufferings.
Thus Mokuren used his holy powers to come to the seat of the Buddha and to inform him of what he had seen with his eyes. He asked, then, what he needed t o do for the women to be saved from their punishments in the pond of blood. The Buddha then answered, teaching Mokuren how t o save the women. He said it would be necessary for them to respect the three treasures of filial piety, to call on Mokuren, to hold a Blood Pool Liberation service, to hold a Blood Pool Feast, to read sutras, to have an esoteric ceremony, then to make a boat and float it off. At that time a five-colored lotus flower would appear in the middle of the Blood Pond. Then, he said, all of the women sinners would be saved, and reborn in the Buddha’s land.
Sweep the dust, Push the dirt 
It seems to still be alive, but not as strong as it once was. The Blood Pool liturgy was only removed from the official Soto Shu scriptures in the 1980s, under pressure from Japanese feminists. So there are still lots of people around who spent years performing and promoting this practice, as well as people who grew up participating in it. One can find temples that still have Blood Pool imagery on their grounds, including on stupas or other objects that continue to receive veneration (indeed, just search Google Japan using the kanji for Blood Pool Sutra and you'll find a variety of examples). There doesn't seem to have been any effort to remove Blood Pool beliefs and motifs from regular temple material culture, just some cosmetic removal from printed scripture books that could fall into the hands of critics. In fact, some temples advertise their premodern Blood Pool imagery as important cultural properties and encourage tourists and pilgrims to visit. It's probably not accurate to pin all of this on Japanese Zen, since the scripture was originally composed in Chinese Chan circles and then imported to Japan via Zen. So we know that Chan monks too acted as priestly mediators, controlling or affecting patrons' afterlives. In fact, such mediation through clerical dedication of merit is still the primary activity of Chan/Zen monks in both China and Japan–it is far more common than, for example, silent seated meditation.
@ Jeff
Thanks for your comments and the information you provided. I thought that this specific topic was of particular interest since many western convert buddhist (WCB) have never seen or experienced Zen Buddhism in this clerical fashion. Neither do most have an understanding of some of the cultural and societal influence that the religion can have or be influenced by.
I did not mean to judge or "pin" anything on any culture (Japanese or otherwise). I don't think that these practices are cultural "baggage" and are in fact important (although this one was alittle over the top for me). I understood that the sutra had its roots in China and Ch'an Buddhism but was unable to find specific references to it.
It would be nice to have more literature available to western readers/practitioners concerning the afterlife mediator role of Zen/Ch'an priests. William's "The Other Side of Zen" is the only one that I was able to find and it is only concerned with the Soto tradition in Japan.
Cheers,