Ok, I'm a newbie but this site has been awesome and a wealth of information. I am currently at the point of replacing all the fuel / overflow lines for my 400F. Some good info all around but not all in one spot so I hope this helps out!
What I found!
1. 3/16 inch I.D. tubing works great for fuel tank to Carbs. Replaces the 5.0 (or 5.5mm I've heard both) great without clips. You only need about 2 feet total of this. You can pretty much find this stuff anywhere! Ebay, Autozone or most auto parts stores. Also is comes in a variety of materials, make sure you get the gasoline or diesel compatible stuff. Cheap too!
2. 1/8 inch I.D. works great for everything else except for the small (1 inch) piece between carbs 1-2 and 3-4. This size (4mm ish replacement, again not sure of the exact size of stock) works for all the over flow tubing coming from the carbs. Again, no clips needed. One this to note though that when you get smaller than 3/6 inch I.D. your selection of tubing becomes very small and you start getting into RC tubing. Again make sure you get gasoline compatible stuff. Not silicone. I have found that TYGON is the easiest to come by in anything less that 3/16 inch. One downside is that is typically comes in a translucent yellow color. I actually kind of like the way it looks on my bike though.
3. 3/32 inch I/D is just a bit smaller and works well for the intra-carb tubing. A little big but its no going anywhere and fits nicely.