We used to have a 65L plastic storage bucket, but lined it with an old bed sheet, and then the lego poured on top.
This means that when the kids want to play, you can lift the entire collection out of the bucket with the sheet, then lay the sheet on the floor.
When they're finished, you pick the sheet up by the corners, and place the thing back into the box. We rarely had orphan parts flying around the house because the sheet both gave the kids a defined "play" area, as well as a much more convenient way to handle a large amount of bricks.
This means that when the kids want to play, you can lift the entire collection out of the bucket with the sheet, then lay the sheet on the floor.
When they're finished, you pick the sheet up by the corners, and place the thing back into the box. We rarely had orphan parts flying around the house because the sheet both gave the kids a defined "play" area, as well as a much more convenient way to handle a large amount of bricks.