Boil your peeled mashed potatoes until they are nice and soft. Then in a very large bowl, start putting the potatoes (one by one) into your ricer. Press down and you should have the potatoes gush out into the bowl. Be careful sometimes this can make a mess.
This will take a while, once all of your potatoes are done you should have a pile of riced potatoes. Add your butter, salt, milk, and mash together. This should be a lot easier because all of the hard work has been done for you.
Serve and Enjoy! If you want to make these a day ahead you can, I would just add some milk and butter to give it some more life.