For full complement of blood cells try diluting 5 ml whole blood in 50 ml PBS. Centrifuge.  Resuspend cell pellet in 50 ml PBS (at this stage a > 100 fold dilution in plasma proteins). Repeat steps until the final desired dilution of plasma left (a greater than 10X dilution is achieved with each step). After fifth centrifugation step should have less than 1 ug/ml plasma protein in cell mixture. Reconstitute to desired final volume.  If you use density gradients like ficoll/histopaque you may lose some cell fractions. 

I can suggest you, that it is enough by following two normal wash with 10 fold volume of 1X PBS to the plasma separated blood pellet.

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Kadar Moideen Abbas

the best at least 3 washing by buffer and centerfugation

First step is centrifugation for plasma separation (from RBCs);

Second, to wash RBCs with PBS two time. 

You can increase the proportion of PBS to 10 to even twenty times during second and subsequent washes if possible, this could reduce time. 

else use filtration through a suitable membrane. this reduces the void volume and carry forward of blood proteins. 

Wash by PBS for 2 times 10 fold washing.