How much salt are you going to get? I read on one website that the rule of thumb is 5 gallons of seawater to 4 cups of salt, which would mean a 5% salt solution. I did 4 gallon batches, and got between 2.5 and 4 cups per batch, which is a bit of a lower yield. However, my small batch of 2 quarts gave me 1 full cup of salt, which is much higher. So it all depends on the original saltiness of the seawater and the method used to evaporate it, and how careful you are not to lose any salt to the floor in the process (I speak from experience—I lost more than I'd like through careless pouring).
Overall, I processed 16.5 gallons of seawater, and I ended up with over 9 cups of salt. This is a total of about a 3.5% yield by volume of salt from saltwater, but your mileage may vary. I documented my own experience on my blog.
Let's get started!
Step 1: The Gather
Go on a road trip to the nearest saltwater source with your containers. You may want to do some research into the pollution along your coast so you don't end up with dirty water that won't give good salt (and may be very bad for you!). Generally, the farther from civilization, the better.
Gather as much saltwater as you like. The more you get, the longer the process will take, but the more salt you'll end up with.