You have to do 'purify mind first'. Let it finish, i.e. wait until the vllager no longer says 'Purifying..'. Any villager coming into the area will abort the meditation so have your finger on the space bar, ready to PAUSE and remove anyone incoming. Having the kiddies in the nursery school helps somewhat.
Then go put the soap in the pond and get clean. Again, be sure you let him finish. And, keep your fire going.