The passages that you are looking for are going to be found at the very beginning of chapter 20, if you want to look them up for yourself.  Mr. Dolphus Raymond was notorious in Maycomb for a couple reasons.  The first is that he enjoyed the company of black women; in fact, he lived with one.   Because of the town's innate racist leanings, and society's views about inter-racial relationships, people considered Mr. Raymond a scandal as a result.  The second reason he is notorious is because he is considered a bit of a drunk, because he always carries a paper sack with a straw sticking out of it, which people assume is liquor.

Well, to Dill's surprise, Mr. Raymond offers Dill a drink of it outside the courthouse during a break in the trial.  Dill accepts, and says, "Scout, it's nothing but Coca-Cola."  So, Mr. Dolphus Raymond goes around drinking coke from a paper bag, making everyone think he is drinking liquor.  When they ask him why he does this, he tells them that he knows people judge him for living with black people, and so he uses the "liquor" facade

"to give 'em a reason...folks can say Dolphus Raymon's in the clutches of whiskey-that's why he won't change his ways.  He can't help himself, that's why he lives the way he does."

So, he keeps up the ruse so that people won't judge him so harshly.  They'll think instead, hey, he's a drunk.  He can't help it if he lives in a way we disapprove of, because he's wasted most of the time.

I hope that helps a bit; good luck!