How did Andy manage to break the wall using a rock hammer, squeeze out into a sewer...

That is pretty much the last half of the film. I think it was a series of rock hammers.

The walls weren't as strong as people thought they were.
He was an accountant, the warden trusted him with the secret books, and it was easy for him to embezzle money.
Breaking into the sewer pipe is a little less likely.

Step 1: Chip away, little by little.

Step 2: Acclimate yourself to the smell and feel of poop.

Step 3: Monularize a paper trail with accounterification.

Simple!

It takes a lot of planning.

There was a scene where he was scratching something on the wall with the hammer. And then a huge chunk of the wall falls out. That scene implies that the wall was in poor condition. That's how Andy was able to dig that huge tunnel with a rock hammer. The walls were disintegrating

It's basic how he squeezed out of the sewer. He broke a hole with a rock, he crawled in, he crawled out

How did he get the money from the warden with that fictitious account? He goes through this point in the library with Red. He was cooking the books for the Warden, so he had a lot of liberty about where to direct the money. He created a fictional individual named Randall Stevens

The question should be, where did he find that rock he used to break the sewer pipe.