How to build a toilet under the sewer level?
This type of toilet pump combo allows you to lift all bathroom waste and water  up to appropriate level so it can be tied into your sewer system. 

Here's a picture of how it sets up.



http://www.saniflo.com/products/index/show-product/lang/en/type/part/id/54

http://www.saniflo.com/?gclid=COLar4KYzckCFUcvgQod11kL4Q