What is the best/easiest way to juice a watermelon? Last year, I had a lot of leftover watermelon from a full-size melon and I pressed it in a strainer to get out the seeds and pulp, but it took forever.

(I then froze the juice in ice trays and stored them in ziploc bags in the freezer - it makes a great margarita in the blender.)

Now that we are getting great local watermelon again, I thought it would be a good use (I've got a huge half a melon taking up space in the fridge)

Are powered juicers any good for this?  Would they work with watermelon (obviously cut up with the rind removed)  Would I have to remove the seeds manually first?

(I found this ridiculous video of Rener Gracie, BTW: http://www.youtube.com/watch?v=ClIepBc7z6s)

Apparently, they claim that the $20 Gracie Juice Bag (http://www.gracieacademy.com/storeitem.asp?r=74903) is more efficient to use on watermelon than the juicer they sell on the site.
The way that i found to juice mine is leave the rind on, mash the melon to bits inside of it, cut a spout in the rind for easy pouring, line my stock pot with chese cloth (although i'm sure a lot of other things would form a great strainer), then just pour the whole thing into the stock pot. I then wrap the cheese cloth up and tie it off with a rubber band. Then you place a plate on top of the cloth and weight it down with a book. Check back every one or two hours to tighten the cheese cloth up and you end up with a lot of juice and none of the nasty bits.  I also tend let the contraption sit in the fridge while it does it's work but it will work just fine on a counter top.  The set up takes me about ten minutes.