Maniac's actions as though the boy were a figure from tall tales, like Paul Bunyan. So, we can findhyperbole featuring throughout the story, adding to the humor and the interest of the events. Let's check out some examples from the chapters you mentioned.

From Chapter 23:

When Maniac finally forced himself from the shower, he found the old man waiting with clothes. Grayson's clothes. "I called the U.S. Army in to haul them buffalo rags away," he said. "They come in with gas masks on, and they used tongs to pick 'em up and put'em in a steel box, and they took the box away to bury it at the bottom of the first mine shaft they come to."

That's Grayson talking, hamming it up as he describes what had to be done with Maniac's stinky clothes. The boy had been staying in a pen with some buffaloes, so he really did smell like one when Grayson took him in! The old man's hyperbolic description adds humor to the story.

From Chapter 25:

Sleazy hotels. Sleazy buses. Sleazy stadiums. Sleazy fans. Sleazy water buckets. Curveballs and bus fumes and dreams, dreams of the Majors —clean sheets and an umpire at every base.

As we read this this exaggerated description of the stories Grayson shares with Maniac, we start off believing in its truth—sure, hotels and perhaps even buses can be sleazy—but then the hyperbole kicks in and we just laugh at what a "sleazy water bucket" would possibly be like.

Here's another example from that chapter:

The batters were teeing off as if it were the invasion of Normandy Beach.

This means that the baseball players were taking the game as seriously as a major war. That's definitely a stretch: an instance of hyperbole that adds drama to the story.

From Chapter 27:

"I'm reading!" yipped the old man. His smile was so wide he'd have had to break it into sections to fit it through a doorway.

The narrator's hyperbolic description of Grayson's excitement as he reads his first sentence conveys the extent of his joy. As readers, we experience his pride and happiness as if it were our own.

You'll find this example in Chapter 29:

Maniac thought of Thanksgivings past, of sitting around a joyless table, his aunt and uncle as silent and lifeless as the mammoth bird they gnawed on.

As he thinks that his relatives were so quiet and unhappy that it's as if they were actually dead, Maniac further characterizes this couple, helping readers understand why he absolutely had to run away from their loveless home.

Here's a hyperbolic description of Maniac's room in Chapter 30:

Santa's elves themselves would have felt at home. Strings of popcorn swooped across the ceiling. Evergreen branches flared at random, dispersing their piney aroma. Wherever there were a few vacant square inches, something Christmassy appeared: a matchbox crèche, a porcelain Santa, a partridge in a pear tree.

We can tell that this is hyperbole because, according to the narration, pretty much every inch of the room had holiday decorations in it. That's almost impossible! The effect of the exaggeration is that we understand the happiness and excitement felt by both Maniac and his friend Grayson as they share the holiday.

Finally, there's some hyperbole to be found amongst the sober sadness of Chapter 32, but it's rather rude:

"I'm freezing my cochongas off," a pallbearer announced.

He means that it's so cold that some of his body parts are freezing and falling off. Of course, that's an exaggeration, and it serves to show how crass and insensitive the pallbearer is, in contrast with the serious grief that Maniac feels.

A metaphor usually compares two things that are, in fact, unrelated, in order to add emphasis or a clearer understanding of just what is being expressed. For example, when someone says, Life is a beach, it is implied that life is fun, just like a day at the beach. Another common example could be expressed as saying, He is a pig. This metaphor implies that he eats a lot or is sloppy like a pig. A simile accomplishes the same purpose but uses like or as in the comparison.

Jerry Spinelli, the author of Maniac Magee, uses both metaphors and similes to bring his descriptions to life. Page 73 in my version of the book is at the end of Chapter 20. One metaphor compares the way Maniac untangles the knot to the way he plays football: He was "dipping and doodling through openings the way he squiggled a football through a defense" (Chap 20). This comparison illustrates how Maniac maneuvers the string to untie the knot. In that same sentence a simile is used comparing Maniac to a "fairytale tailor." By using these comparisons, Spinelli brings Maniac's actions to life.

A metaphor is a figure of speech that makes a comparison between two unlike things.  One other rule about metaphors is that they cannot use the words "like" or "as" to make the comparison.  If either of those words is used, then the comparison is a simile.  

Page 73 might be a little bit different depending on what text edition you have.  In my version, page seventy three is the very last page of chapter twenty.  Maniac Magee is just about finished untying Cobble's Knot.  The very last paragraph of the chapter has a metaphor that describes what the crowd's cheer was like after Maniac finished untying the knot.  

". . . a huge roar went up, a volcano of cheers."  

The metaphor comparison being made on page 73 illustrates that the crowd's cheering roar was super powerful.  How powerful?  It was basically a volcano exploding.  

Hyperbole is a literary tool that uses an exaggeration of an idea in order to create a larger emphasis on it for the reader. In pages 27–29 of my edition, readers see hyperbole being used when the narration is explaining about all of the things that Maniac Magee likes about his new life and new community. One example that we are given is about the Fourth of July and how much Maniac loves it. He likes it a lot because the "whole East End" shows up for the day. This is hyperbole because there is likely at least one single person that did not show up for one reason or another, but it gives the emphasis that a lot of people from that part of town showed up.

Another hyperbole from those pages tells readers that Maniac Magee scored a lot of touchdowns in their pickup football game that he was playing with Hands Down. Hands Down picks Maniac, and everybody laughs at his pick because Maniac is so young looking; however, Maniac amazes them all with his ability to run routes well and catch anything that Hands Down throws near him. By the time that dinner is called for, Maniac supposedly scored 49 touchdowns. That's just crazy. That's 294 points scored by one guy. If Maniac scored a touchdown every 10 minutes, it still would have taken him over 8 hours to score all of those points.