Trust me... I've looked into them... I'm in this industry.
There are no supplements out there that enlarge anyone’s privates. If people say it works it's a placebo. People want to believe... and if you take something believing your you know what will grow bigger... you will think it actually did. But take out a tape measure... same results as before... nothing changed.
If you get HBO, try watching Pen and Tellers (sp?) show. They usually pick a topic and make fun of it. They've done similar shows about this topic doing their own studies and showing how people think it really works and are willing to spend $$$... but in actuality nothing actually changed.
Drinking milk as a youth can help strengthen your bones. I'm not sure how much that helps as an adult but I know it does much less. I have never heard of milk actually allowing someone to grow taller... and I know of no study being able to prove that. You are genetically determined how tall you can grow. The only thing you can do physically is stunt your growth (not grow as tall as you should have genetically).
Stretching or (hanging) until your arms give out will not make you taller. Height is determined by your bones... nothing else. There is nothing you can physically do to lengthen the size of your bones besides having a doctor cut you open and install a "bone spacer" or something. I wouldn't recommend that

.
As far as different heights during the day, that's simple. When you wake up you are alert and your muscles allow you to stand more upright... but after a long day you are tired and you tend to slouch a bit more. Think about a person who doesn't workout. Now put him in the gym for a good month or two. Chances are he will have grown 1-2"... but he didn't... he just increased his posture and stood more upright. There's pockets of air in our spines... but that air isn't making us taller or making us smaller. When you crack your knuckles do your fingers grow an inch longer?
I can find a bunch of people out there that say they been abducted by aliens... or they had cancer and ate nothing but Snickers and the cancer disappeared... or, like we're talking about, have drank gallons of milk and increased their height. My point is, these peoples claims were not backed up with scientific proof. There's so much BS information out there you have to be careful. If you want to believe that doing these "hangs" or drinking lots of milk will increase your height... then that's your choice. Scientifically if there's no proof to back up these stories... then I'm not willing to waste time on money on them.