Muck does not want to be alone guarding you two. He wants a gun for his safety.

Indeed. Zoon owns a gun. Give the gun to Tuck.

Isn't he a sissy. Well, you know what to use: Gunpowder!

Hmm.. who sells rockets?

Go to Burnert's and grab one of the rockets.

Use the shard of glass to get the gunpowder out and put the gunpowder into the gun. Maybe this will ease Tuck.

Isn't he something. You should use some small stuff as an ammo.

Use the small junk you got from one of the balloon bags as an ammo. How about now?

You could stuff the ammo into the barrel with something like... a bottle brush?

Great! Use it on the gun with the ammo and powder. It is now lock and loaded! Give it to Muck.

Finally. Now you and Mac can enter the tunnels.