"...........with the problem with getting rid of the residual product, that is now in contact with the fresh oil."
No need to get rid of the residual product if it is drained correctly, it will be a minute amount compared to the volume of oil in the engine and won't cause a problem, if it could Comma would warn about it.
No one worries about the residual old oil contaminating the new oil after a normal oil change. ��
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