What did Max do when the grate would not open?

Max did exactly what Freak told him to do.

He reaches inside his little cape. Out comes a flashlight, one of those small kinds that look sort of like a cigarette lighter, and also a spool of kite string.
“I devised a special retrieval device,” Freak says.
“Looks like a bent paper clip on a string,” I say, and Freak tells me to shut up and follow orders.
“You hold the string,” he says, and then he gets down on his knees and shines the little flashlight through the grate. “Can you see it?” he asks. “Can you?”
I look, but it’s hard to see anything and it smells like something died in the storm drain, which come to think of it, it probably did. Rats or worse.
“Down there,” Freak says. “The beam is hitting it right now.”
“That? That’s just a piece of junk.”
“Wrong,” Freak says, real fierce. “It looks like a piece of junk. It may very well contain fabulous wealth. Drop the line down and see if you can hook it.”
I’m thinking, boy, what a butthead, rolling in the dirt for this little Darth Vader so he can play pretend games in the middle of the night, but I do what he asks, I drop the hook down, and much to my surprise, it actually hooks into something and when I pull up on the kite string I can see what it is.
“A purse,” I say. “Looks like a grotty old purse.”
“Careful,” freak says. “Pull it up to the grate so I can grab the strap.”
I bring it up an inch at a time, and Darth – excuse me, Freak – manages to get his small hand down through the grate and grab hold of the soggy old purse and then he almost drops it. I yank it up on the kite string and we both manage to squeeze the slimy purse up through the bars.
“Whew! Mission accomplished,” Freak says.