I can.. just finished helping do one for my son and I've done several in the past. If you are going for the creek look, you can get away with putting a small peice of pond liner or plastic in the 'pattern' of the creek first and line it with small stones to hide it. It looks great if you do it right. Just use stones that scale well with the size of the stream for the most convincing look.
Now to drain it..
It depends on what you want to accomplish. If you are running the sloping stream into a small 'pond' then you'll need a glass, acrylic, plexi divider and run a pump with tubing back to the start of the stream. You can try and stack some rocks, wood, etc to hide it, but it usually ends up looking a little unnatural if you don't hide the divider well.
What a lot of people do is do fill the tank with about 3-4" of gravel. (which you should do anyhow for drainage). Add your soil over top of that. If you do it that way, you can use a rock slope down into the 'pond' area. If you do not wish to have a 'pond' area, you can just keep soil off the spot where the stream ends so it drains back into the gravel. The advantage of doing it this way is that the pump can be hidden anywhere in the vivarium in the gravel. I used a peice of blue filter foam media and wrap the pump before hiding it. Make sure you do locate it where it can be removed and serviced if needed.
Lastly, think about the pump placement and where the stream starts ahead of time and before you do any background work. If you are using a "Great Stuff" foam and silicone/coco-fiber background, consider where your stream will start and run the plumbing ahead of time behind the background so it'll stay out of sight. Doing it that way can give you many options for waterfalls, streams, and you can even tee off the main line so you can add additional tubing to serve as a trickle waterer for different plants like bromeliads, etc. (just make sure you run the tubing to an adjustable flow valve like an aquarium air-line valve so that you can adjust how much flow you want out of the trickle waterers).
I'll try and add a pic of my son's vivarium we just did last week to give you a better visual. It's a little too late to get it tonight so I'll attempt it tomorrow.