the lava rock was used for two reasons one it was cheap and available on a sunday two is after great debate we found that the scrubies were being forced into the outlet end under pressure and slowing flow considerably,even with a grate installed. so maybe not the final media but being used on this test run. the tube is about 2" higher on the outlet end to help remove traped air. the air comes out in small surge bubbles about every ten seconds when the is air on. and yes it is on. i also have never seen this done hense all the ?'s it just seems too simple not to work. and i am still tring to get home to get the pics hopefully today otherwise tommorow morning