Mizu ni nagasu (水に流す): to let it flow away in water. To treat past troubles as if they had never happened.
Ame futte ji katamaru (雨降って地固まる): after rain, the ground hardens. After a quarrel or a hardship, things are on firmer ground than before.
Uramikko nashi (恨みっこなし): no grudges on either side. Said before a result is known, as in dō iu kekka ni natte mo uramikko nashi ni shiyō, whatever the result, let us hold no grudges.