Yes it is supposed to be a clear tube. They often seem to be painted over or so dark you can't see the fuel.
When it is clear you will be able to see the fuel as it moves down the tube from usage. If you can't see fuel it is either really full or nearly empty - you kind of have to know which it is or look in the fuel cap to see if it is full.
There is a nipple at the top and the bottom of the tank, about a half inch to one inch from the top and the bottom. They are bent 90 degrees as they come out of the tank, top points down, bottom points up (go figure!). The nipples have a little bulge in them near the end.
The tube slips over that and is held on with these little wire rings. The rings are two or three turns (in a helix like screw threads) that clinches the tubing tight so it doesn't leak. I have no idea how they are supposed to be installed (professionally). I took two small screw drivers and pushed the ends toward each other so the hoops expanded enough to get over the bulge in the tubes. It was frustrating and time consuming so I assume there is a better way to do it. If you heat the tube up in warm water (blow it out before installing it) it will shrink (in length) and be a tighter lengthwise tube after it cools down.
All the parts are a few dollars (less than $5?) from the dealer. You can probably get the tubing from the hardware store. I guess you could use small wire ties to cinch it tight.
Time your fueling and you won't have to drain the tank to do this. But don't run completely out!