From the study:
Tired & Poor: Bankrupt Arguments for Mass, Unskilled Immigration
We at the Center for Immigration Studies estimate that the average Mexican immigrant will use $55,200 more in public services during his lifetime than he pays in taxes. In effect, Mexican immigration acts as a subsidy to businesses that employ unskilled workers, holding down labor costs while taxpayers pick up the tab for providing services to a much larger poor population. It's like any other subsidy: Businesses that receive it want it to continue, but for the nation as a whole, it's a bad deal.
More like, one or two living in the house will be paid under the table and be able to pay the mortgage for the other 10 - 15 living in the same house. All the while, the taxpaying citizens will pay for their social services.