Corrected entry: When Hector is singing to his forgotten friend, he takes a drink and the drink doesn't exit his body...where does the liquid go?
Corrected entry: After Coco died Hector should be forgotten and disappear from the land of the dead because his daughter was the only person who knew him in life, even from pictures according what he said to Miguel about Chicha.
Correction: According to the rules of the film, it's not that someone had to have known you in life, it's that you are remembered. That's part of the plot; Hector will disappear because Coco is the only one who remembers him. When hearing her father's music "brings her back" she starts telling the family stories about him, so he'll continue to be remembered.
Correction: In addition, Chicharron has already been forgotten. He can't come back just because Miguel remembers him from the land of the dead.
Correction: It is safe to say this film chose for the laws in the land of the dead to not be followed the same way they are with the living. While it is scientifically correct that the liquid should go somewhere; if we get that technical the film would be a mistake in its entirety as the skeletons should not be able to talk, walk, or drink at all without muscles and other organs. When the entire nature of the film is fantasy, artistic license allows suspension of the laws of real life science.