Whether the Seller connects to the sewer is a negotiable point and as Jason mentioned there may be requirements depending on your financing choice.
However, this like all aspects of a purchase is negotiable. Having a good Broker is certainly helpful in a situation like this.
Assuming you want to be connected to the sewer and/or your financing choice requires it you'll simply want to build that point into your purchase contract. If you have already entered into a purchase contract that contract will answer your question.
From time-to-time the city or county may send notice of a required deadline in which a homeowner has to connect to the sewer line (referred to as an assessment). If that notice has been given to the Seller (anytime prior to closing), and the Seller has not yet connected, the Seller is required to disclose this fact in the Disclosure Statement (assuming your contract required one to be prepared).
To better answer this question I'd need to know what stage your contract is in. I hope this helps!... more