the man who had drunk

[Navi]

Which are correct:

1-In the bar, there was this man and we didn't know how much he had drunk. He fell unconscious.

2-In the bar, a man about whom we didn't know how much he had drunk fell unconscious.

3-In the bar, a man that we didn't know how much he had drunk fell unconscious.

4-In the bar, a man that had drunk we didn't know how much fell unconscious.

I think 1 is OK but is very informal.
4 is probably acceptable but seems to me to imply that he had drunk a lot.

[Dozy]

#1 is OK in an informal conversational style.

#2 is ugly.

#3 is incorrect.

#4 is possible in conversation but looks a bit awkward written down, probably because it loses the guiding intonation. I prefer "who" to "that", but people do use "that". You're right that it tends to imply that he had drunk a lot.