As water drain away slowly, I turned the stopper (round one) a bit (less than 2-3 centimeters), the water quickly is gone, but the stopper didn't lock, just open. This happened all of a sudden this morning. I've lived this apartment 13 month without any problem. Please let me know how to fix by myself if anything I can do...Is this a serious or need any parts? I would appreciate your advice or any help million, forever!!