Hi everyone!

So i got into this because I'm a welder and friends are always asking me to weld stuff for them, so feel free to laugh at some amateur questions. I cant upload a picture for some reason, but I was curious about the K100 gas tank. There are 2 lines on the upper left hand side underneath the bike. I''m assuming those are to the fuel rail and fuel pressure regulator? Does anyone know what to other 2 are that are more towards the middle lower portion of the gas tank? 

Any help would be great!

Rainwater and fuel vapour.

awesome so I don't have to hook any lines up then im assuming. Do you know which one on upper left is fuel rail?

Rearmost - if you follow the lines inside the tank this will come from the fuel filter - after the pump.
The front pipe is just the return and may/may not have a pressure relief valve in it depending on model year.

The two smaller pipes that you queried are both vents - follow the lines inside the tank and one will be a drain from the recess around the filler where rainwater can collect. The other will be the tank vent. Both usually connect to pipes draining near the centrestand. You might not be worried about a bit of rainwater , but I'd recommend making sure the fume vent is properly piped away - on a hot day you can see the fumes coming out of it!

Water drain hose and the fuel expansion hose can also drain into small catch tray that clips onto the frame rail. It should line up with the spigots from the tank. a single hose then runs down to a point near the rear brake master cylinder.
Regards Martin.