300DT fuel line leak

1984 300D Turbo fuel leak near tank. I have purchased the two sections of line (different sizes), but it's tricky to access (up above differential and rear axle).
Picture here:
http://static.flickr.com/119/274184602_d7321608cd_o.jpg
The leak is in the smaller of the two lines, but I plan to replace both. Some say you must drain all fuel to replace these, others say you can clamp the hose, remove one side, fit the new hose, then attach the other end quicky. Anybody do this? I want to know which direction the fuel flows in these two lines so I know which end to remove first. I am guessing the fuel flows from tank to engine in the large line, and vice versa in the small line. Is that correct?
Also, how do you replace the fuel filter that's inside the tank? Thanks in advance.
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Um, the setup does not look like W126 so my experience may not apply.
I did replace the two rubber fuel hoses on 87 300SDL. One end of the hose has the metal fitting, sort like the high pressure power steering hose. The other end uses clamp. I burned up the fuel. As to the inside mesh filter, it's 46mm socket size (again, this may not apply to W123).
I am working on a in-tank fuel pump on a Chevy. This time I regret I did not drain or use up the gas. It is messy. I plan to drain the gas before putting it back though I haven't found a good and inexpensive hand pump yet.
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Finished the job. Pumped the fuel out of the tank first, which resulted in absolutely no drip when I replaced the hoses. Clamps were extremely difficult to remove. Phillips screws are such a stupid thing to use here, because of the corrosion, and because the clamps move away from you when you apply force, so the driver just rides up and out. Replaced them with hex-head clamps. Mercedes dealer gave me the wrong size hoses, and that was a pain to find out when everything was taken apart. &%*@#!!! No problem starting the car when fuel was replaced. Diesel fuel really eats an asphalt driveway. Don't recommend spills or leaks there.
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