Another method, (Dave's is good, but just a different way of doing it, so you have more options) we use pretty thick sponges, cut a hole in them lengthwise in the center and slip them over the intake valve. That provides more surface for bacteria, a good place for microfauna for the babies, and keeps the current down.
As for getting poop off of the bottom, buy a very thin length of airhose. Like the width of a pea or something nearly that small, and siphon out into a bucket. You can go slow along the bottom of the tank and get the fecal matter without running too much of a risk of getting the babies, and if you are draining into a bucket you can pull out any babies that choose to take the rollercoaster of fun.
