Flushed Away
(2006)

The Toad's plan is to raise the FloodGate and wash away all the sewer rats once he gets the Master Cable back.  Rodney gets back "up top" to his home but realizes the Toad's plan and flushes himself back down the toilet to save the day, leaving Syd to take his place.  He breaks the pipeline of Liquid Nitrogen to stop the water coming through the floodgate and rescues the girl. 

Thanks Sharla!