The instruction to drink the blood of the Son of Man is first given in John 6:53:
εἶπεν οὖν αὐτοῖς ὁ Ἰησοῦς· ἀμὴν ἀμὴν λέγω ὑμῖν, ἐὰν μὴ φάγητε τὴν σάρκα τοῦ υἱοῦ τοῦ ἀνθρώπου καὶ πίητε αὐτοῦ τὸ αἷμα, οὐκ ἔχετε ζωὴν ἐν ἑαυτοῖς [NA 28]
Most translations express the negative μὴ at the beginning of the verse ("not eat the flesh") in terms of a positive command. For example the ESV:
So Jesus said to them, “Truly, truly, I say to you, unless you eat the flesh of the Son of Man and drink his blood, you have no life in you.
Young’s Literal Translation retains the negative language:
Jesus, therefore, said to them, `Verily, verily, I say to you, If ye may not eat the flesh of the Son of Man, and may not drink his blood, ye have no life in yourselves.
However, there is no second "not" before "drink his blood" and the literal translation is:
Jesus, therefore, said to them, `Verily, verily, I say to you, If ye may not eat the flesh of the Son of Man, and may drink his blood, ye have no life in yourselves.
This seems to describe a different condition, namely someone who has not eaten the flesh but has drunk the blood. The next verse makes it clear both eating and drinking are required, so the outcome, "have no life in you" is not changed because someone only drank.
The next verse appears to be restatement where the requirements are given in positive terms:
ὁ τρώγων μου τὴν σάρκα καὶ πίνων μου τὸ αἷμα ἔχει ζωὴν αἰώνιον, κἀγὼ ἀναστήσω αὐτὸν τῇ ἐσχάτῃ ἡμέρᾳ.
Whoever feeds on my flesh and drinks my blood has eternal life, and I will raise him up on the last day. (6:54 ESV)
What exactly is the difference between eating and drinking in the two statements?