“What have you gotten us into? I should never have let you talk me into this. You and your big ideas!” Trent mumbled, half to himself, I would think you could cut 'half to himself' because 'mumbling' already implies that he's talking half to himself. as he followed Andy down the narrow tunnel.

“No really, this is real! I swear! This time I’m sure as the nose on my face!”

“That doesn’t even make sense, sure as the nose on your face? What does that even mean?”

“Just trust me! I heard Terry tell Shannon that he heard a woman walking by their yard telling another woman that she saw it with her own eyes!”

“So why then didn’t those ladies take it? Or Terry, or Shannon even?”

“Well, Terry and Shannon can’t get out of their yard, of course. And the ladies probably thought they could sneak in later, after their walk maybe. They didn’t know Terry heard them!”

“Ladies couldn’t even fit down this pipe, how did that lady see it?” Run on sentence here.

“From the bridge I guess? Anyway, she probably has a car, they all do, and when they get to it she’ll drive over! This pipe is a shortcut!”

The light at the end of the tunnel was finally getting bigger. Line break here. “What is this place anyway?” Andy asked.

It’s just where the extra rain collects. People toss stuff down from the bridge all the time thinking nobody will see it, but it’s usually tires or old computer screens. Every now and then something good though, so I come here sometimes and check. Is he talking or thinking? There's no quotation marks here, so I'm not sure.

They got to the end of the tunnel and looked out.

“Yes!!” Andy hooted. It's almost always better to use plain, boring dialogue tags (said and asked.) The fancy ones can pull readers out of the story. If you want to keep 'hooted,' I would suggest rephrasing. Andy hooted. "Yes! “We got here before the ladies came back! Look at that!!”

“Well, I guess you were right this time!” Trent said, as the two dogs rushed out, excitedly, to the smelly, broken bag of garbage strewn across the ground. Ohhh!! I am pleasantly surprised! How cute :)