I used to collect the RO waste water in top load washer, but I got a lot of grief from people in the house complaining they cannot do their laundry. So that was not worth it.
As for collecting it in a container outside the house, make sure it does not become a mosquito breeding ground (e.g. zika).
Right now, it just goes down the drain. I just do less water change instead, half what I used to. I'd say most people are probably doing too much water change.