"Bottom of the hall" is not correct, but "at the end of the hall" is. "Down the hall" is also correct, but it could mean anywhere in a given direction, it does not necessarily mean "at the end of the hallway".
"His office is just down the hall." - His office is further along in the hallway, in a direction pointed out by the speaker. "Down" here just means "along" in a particular direction.
"The bathroom is at the end of the hallway on the left." - The bathroom is actually the last or one of the last doors in the hallway, and it is located on the left-hand side.