This is essentially a non-re-circulating active system that is usually a drip irrigation set up. This method is commonly used for large scale commercial hydroponics.
Run-To-Waste works by the nutrient solution running into the growing media from a single reservoir via an irrigation system and drippers, sprayers or sprinklers. Ideally there needs to be a certain amount of run-off (about 25%) on a daily basis, as this helps to refresh the media content continually. This method nearly always uses timers.