A dialysis system with a flow path insulator is disclosed. The dialysis system includes a cycler and a disposable set including a patient line and a drain line. The cycler pumps fresh dialysis fluid to a patient via the patient line and used dialysis fluid from the patient via the drain line. The dialysis system also includes a flow path insulator provided at or by at least one of the cycler, a water purifier, a dialysis fluid preparation unit, or along the drain line. The flow path insulator includes a first valve operable with a first fluid line and a second valve operable with a second fluid line. The first and second fluid lines lead to a chamber. The flow path insulator further includes a pump positioned and arranged to pump used dialysis fluid from an outlet of the chamber to a second chamber.