Dav Pilkey 
Captain Underpants and the Attack of the Talking Toilets [EPUB ebook] 

Not so long ago, George and Harold created the greatest superhero in the history of their school – and brought him to life by mistake! He is Captain Underpants, and his true identity is so secret, even HE doesn’t know who he is! But that was only the start… Now the boys have accidentally created a whole army of evil, vicious talking toilets intent on taking over the world!!! Someone needs to flush them out – and it’s DEFINITELY a job for the world’s ONLY superhero with WEDGIE POWER!