I'm not sure about the clamp issue, but after we filled our tank using the garden hose and checked for leaks, my husband just siphoned the water out using the hose, it worked out great. Of course my tank is next to a window that just happens to be next to the garden hose.
When you start mixing the salt, I would recommend NOT doing it in your tank. I ran into a bad batch when I was mixing the saltwater in my QT, and had to dump the whole thing, luckily it was just a 10 gallon tank. So I used a 20 gallon trash can and started mixing away. Took a few days, but it will be worth it if you run into a bad batch of salt.
OH, and congrats on getting things rolling!!!! Can't wait to see it up and running!!