Ratman is hiding in the sewer with his loyal rats and stinging flies. To defeat him, you have to get past them.
The procedure :
Defeating him has nothing to do with milk. There is no milk to be found anywhere on Super Power island.
Ratman is hiding in the sewer under City Park, with his pet rats and stinging flies.
Ratman is on Super Power Island. There is a large rat in the sewer entrance to the factory on 24 Carrot Island (climb up into the bypass pipe to elude him).
u spin the weel and a bunch of gunk comes out
Turn the red wheel on top of the last ledge.
You don't catch them in any set order. You can start with Copycat and Speeding Spike at Downtown, Sir Rebral and Ratman at City Park, or Crusher at the Junkyard. (see the related question)
There is no jetpack on Super Power Island, as there is on Early Poptropica. The ability to fly is an actual "super power" on the island, and is only acquired by defeating the first five super villains (Copycat, Speeding Spike, Sir Rebral, Ratman, and Crusher), using your wits only. The pay phone will then ring and give you flying power, which you need to catch Betty Jetty. (Super Flying Power works only on this island, but comes in handy on the various ad games, when they are accessed from Super Power Island.)
Both restrooms (boy and girl) lead to the sewer where Ratman is hiding.
When you face ratman and his rats and flies, climb to the red wheel at the upper right, which will dump sludge on Ratman. Jump quickly between the rats. Then avoid his flies to jump over to him and cuff him.
The toilets in Poptropica are decorative, except that the restrooms on Super Power Island lead directly to the sewer where Ratman is hiding.
In the restroom at City Park, there is a drain that leads to the sewers where Ratman is hiding. (see related question)
Ratman is one of the six escaped super villains. Ratman is found in the sewer. You get there by going into the toilets and down the manhole on the right side. When you get there just swim until you get to a red wheel. Then click on it. It will make the water go up or down. Fiddle with it until you get the right height for the door on the left. Enter it and then you should see ratman.