If he started one on each tank for this it be the 4th thread. Plus this way we can look back and see what he was doing with his other tanks be for he set this one up so if this has truble you dont have to go hunting down all 4 threads.
The only time it is bad is if you let it set and then move it or mess with the sand. If you keep the sand moving as far as I know it will not build up the waste pockets.