Be sure to scroll down... there may be more than one question on this page!
Your contractor should seek psychiatric help. What sort of insane person would drain a sink beneath the slab of a home? There are some plumbing applications that are approved for this sort of sub-slab drainage, such as the condensate from air conditioners or the overflow tube from a water heater. Both of these are legitimately "low volume"... though even these applications may not be approved if you live in an area that requires year round AC. I see from your address that you don't.
This is a "big time" violation of the plumbing code. Think about it... how can you or anyone else know how that sink will be used? That is what the plumbing code is for... to cover all ranges of normal use. The plumbing code was developed to protect us from the dangers inherent in the waste water leaving our sinks and toilets… both biological and chemical. This improper draining of large volumes of contaminated water will over time erode the soil under the foundation, increase the level of moisture in the basement and introduce water-borne bacteria or other chemical dangers into your basement's environment… the last thing you want to do!
Though I am not an attorney (nor do I play one on TV), I would bet that you would have a legitimate gripe to get back to install the sink properly. How this abomination passed a building inspection is beyond me!
If you have plans of installing a bathroom in the future, you can purchase a kit that is designed to drain a toilet and a sink, pumping the waste water up to your main septic drain. The toilet connects right to the base of the pump tank, giving new meaning to the nickname "throne"!! Read the "Toilet, up flushing" article at this website for more info.
Of course, if you know that a sink is the limit of your basement plumbing needs, you can purchase a smaller pump designed to handle the drainage from a single sink.
Good luck with your attorney!! I have to go lay down for a while.
(NOTE: RP sent a follow-up to inform us that he had some other problems with the contractor last year and tried to get some legal satisfaction. Unfortunately, the contractor had declared bankruptcy. Did this surprise anyone??)