A dialysis system comprising: an extracorporeal circuit including a dialyzer (20, 30), an arterial line, a venous line, a drip chamber, and a blood pump; and a dialysis fluid flow path including a first balance chamber, a second balance chamber, a fresh dialysis fluid pump in fluid communication with first and second fresh compartments (344a, 344b) of the first and second balance chambers (340a, 340b), respectively, the first and second fresh compartments (344a, 344b) in fluid communication with a fresh dialysate fluid inlet of the dialyzer (20, 30), and a spent dialysis fluid pump in fluid communication with first and second spent compartments (342a, 342b) of the first and second balance chambers (340a, 340b), respectively, the spent dialysis fluid pump also in fluid communication with a spent dialysis fluid outlet of the dialyzer (20, 30); and wherein the system is configured to run a priming sequence in which the arterial line is connected to the venous line, and that: (i) uses at least one of the fresh and spent dialysis fluid pumps (370, 390) to pump dialysis fluid through the dialyzer (20, 30) and into the extracorporeal circuit, (ii) uses the blood pump to circulate the dialysis fluid through the extracorporeal circuit in a reverse direction until the drip chamber is filled and vented with the dialysis fluid, and (iii) uses the blood pump to circulate the dialysis fluid through the extracorporeal circuit in a normal operational direction until a specified priming volume of the dialysis fluid is removed from the drip chamber, wherein each cycle of (ii) and (iii) causes at least some of the dialysis fluid to be back-filtered through the dialyzer (20, 30), and wherein the blood pump repeats (ii) and (iii) until the extracorporeal circuit is filled with dialysis fluid. an extracorporeal circuit including a dialyzer (20, 30), an arterial line, a venous line, a drip chamber, and a blood pump; and a dialysis fluid flow path including a first balance chamber, a second balance chamber, a fresh dialysis fluid pump in fluid communication with first and second fresh compartments (344a, 344b) of the first and second balance chambers (340a, 340b), respectively, the first and second fresh compartments (344a, 344b) in fluid communication with a fresh dialysate fluid inlet of the dialyzer (20, 30), and a spent dialysis fluid pump in fluid communication with first and second spent compartments (342a, 342b) of the first and second balance chambers (340a, 340b), respectively, the spent dialysis fluid pump also in fluid communication with a spent dialysis fluid outlet of the dialyzer (20, 30); and a first balance chamber, a second balance chamber, a fresh dialysis fluid pump in fluid communication with first and second fresh compartments (344a, 344b) of the first and second balance chambers (340a, 340b), respectively, the first and second fresh compartments (344a, 344b) in fluid communication with a fresh dialysate fluid inlet of the dialyzer (20, 30), and a spent dialysis fluid pump in fluid communication with first and second spent compartments (342a, 342b) of the first and second balance chambers (340a, 340b), respectively, the spent dialysis fluid pump also in fluid communication with a spent dialysis fluid outlet of the dialyzer (20, 30); and wherein the system is configured to run a priming sequence in which the arterial line is connected to the venous line, and that: (i) uses at least one of the fresh and spent dialysis fluid pumps (370, 390) to pump dialysis fluid through the dialyzer (20, 30) and into the extracorporeal circuit, (ii) uses the blood pump to circulate the dialysis fluid through the extracorporeal circuit in a reverse direction until the drip chamber is filled and vented with the dialysis fluid, and (iii) uses the blood pump to circulate the dialysis fluid through the extracorporeal circuit in a normal operational direction until a specified priming volume of the dialysis fluid is removed from the drip chamber, (i) uses at least one of the fresh and spent dialysis fluid pumps (370, 390) to pump dialysis fluid through the dialyzer (20, 30) and into the extracorporeal circuit, (ii) uses the blood pump to circulate the dialysis fluid through the extracorporeal circuit in a reverse direction until the drip chamber is filled and vented with the dialysis fluid, and (iii) uses the blood pump to circulate the dialysis fluid through the extracorporeal circuit in a normal operational direction until a specified priming volume of the dialysis fluid is removed from the drip chamber,