The full solution is at the related question below.
The key once you reach the Sewer Control Room is that you have to jump up between the rats at the upper right side. They move back and forth at the same speed, so you can jump past one, then the second, then the third, then quickly up to the red wheel. Once you click on the red wheel, the rats are the least of your problems because the flies attack you. Run quickly to the right, Dodge the flies, then back to the left and jump up on the big pipe in the center. From there, you can jump over to where Ratman is.
(see related question)
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).
Defeating him has nothing to do with milk. There is no milk to be found anywhere on Super Power island.
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.
u spin the weel and a bunch of gunk comes out
Turn the red wheel on top of the last ledge.
You have to make a series of three jumps between the rats to reach the red wheel at the upper right (to dump the sludge on Ratman). Then evade the flies and jump from the middle raised pipe over to cuff Ratman.
Once you enter the control room, climb past the rats at right to reach the final red control wheel. This will dump sludge on Ratman and the flies will attack you. Dodge them until you can jump to the large center pipe, and then to Ratman.
Both restrooms (boy and girl) lead to the sewer where Ratman is hiding.
You have to jump past the three at the upper right, to reach the red wheel there. This dumps sludge on Ratman and the flies attack you. Jump past them to the large center pipe, and then over to Ratman.
Once you have dumped sludge on Ratman, his rats run away. But the stinging flies will attack you. Avoid them long enough to jump to the large pipe at the center, then over to Ratman. 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.