What are the exact instructions of the rite of circumcision, particularly about Metsitsa Bpeh (oral suction). How is this requirement follow the laws about blood?

The procedure is as follows:
The proper amount of foreskin is measured that will be removed (enough to ensure that it will not encroach or cover the head of the penis). It is removed with a knife (or scalpel) the inner foreskin (a elastic membrane which is the extension of the outer foreskin) is split as well.

Then, the Mohel (circumciser) applies suction to the wound orally (a Talmudic tradition that without the suction it would medically jeopardize the baby). The baby is then bandaged.

From your question I see that your focus is on metzitza bpeh (oral suction). This for the most part is no longer the practice since there are reasonable claims to its being counterproductive. It is not part of the ceremony rather part of the medical aspect of the bris. That is, according to the Talmud a necessary component to ensuring a safe healing process for the baby. Modern day medicine however indicates that with communicative diseases (e.g. herpes) and the like, oral suction not only doesn’t help the baby it might endanger it.

Mohels still perform the suction to keep to the Talmudic tradition, but not with direct oral contact rather via a sterile tube that has one way suction.

As far as the seeming incongruity of a Mohel taking blood into his mouth when the Torah clearly forbids the consumption of blood (and rabbinically extends to human blood). This is only if the blood is actually consumed. The Mohelim who do oral suction, mitzitza bpeh, spit out the blood immediately afterwards and rinse their mouths (usually with wine).

Just to lend credence to what I’ve told you above, I am a practicing Mohel in Maryland (www.bris.us serving MD, DC, VA, PA). So you heard it straight from the Mohel’s “mouth”.