Depends how caked on and congealed the former contents are, how well the new and old mix, and with how much force you're pouring... Also, if the cup was filled

Depends how caked on and congealed the former contents are, how well the new and old mix, and with how much force you're pouring... Also, if the cup was filled with rat urine before, how much tea would be wasted before you considered it replaced enough to drink? Analogies only go so far.