Is it correct to be satisfied with the strong probability of the impurity being removed by an abundance of water, despite not being certain of its removal or knowing the required number of washes?

It is clear that the questioner is afflicted with waswasah (obsessive whispering), and one must be careful not to give in to it, as it leads to great evil. For the removal of impurity, a strong presumption is sufficient; certainty is not required, because considering certainty here would be a hardship, and hardship is negated in Islamic law. If the impurity is hukmiyyah (non-material, like the state of ritual impurity), then it is sufficient to pour water over it and overwhelm it with water until its removal is strongly presumed.