Conn. Gen. Stat. § 12-412j

In any sale at retail of any new or remanufactured part of an item of tangible personal property to a purchaser, which sale is made by a retailer of such parts who will accept in return from such purchaser a core component or core part of such tangible personal property, the sales or use tax with respect to such sale shall be imposed on the difference between the purchase price and the amount allowed by the retailer on the returned core component or core part, provided the retailer shall collect the tax, at the time of sale, on the purchase price and, when the core component or core part is returned, shall refund such tax on the amount allowed by the retailer on the returned core component or core part. When any such core component or core part traded in is subsequently sold to a consumer or user, the taxes imposed under this chapter shall be applicable to such sale.