Okay, you need to get either rubber fuel hose, or the clear stuff that you mentioned, it needs to be the same diameter inside, as the outside diameter of the metal fuel line. One quarter inch or 6 mm would be best. A small in line filter that has the same sizes on the barb fittings on either side is needed as well, the flexible tubing will go over these fittings,l. Install about 1 1/2 inches of this line on both sides of the filter using a Jubilee Clamp of appropriate size. then measure the length of the filter, take about 1 1/4 inches off this measurement and cut out that much of the fuel line with a tubing cutter. this will give you 5/8 inch on each side to overlap the tube at the gap that is created in the metal tube. if you can have more flexible tubing over the metal it would be even better. You need 2 more Jubilee Clamps. Loosen each clamp and put it on the metal tube on each side of the gap where the filter is going to be placed. Then install the fuel filter by pulling the flexible hose evenly over the metal tube on both sides of the filter. Bring each Jubilee Clamp over close to the end of the flexible hose and tighten both of them.
You can put more hose if you like and cut a longer piece out of the metal tube, just be sure you have enough flexible tubing to bridge the gap with enough going over each end to clamp it. You may also need to look at the filter and see if it has a direction of flow. Some have an arrow on them which is directed toward the Carburator. When you purchase it, ask the folks who sell it to you about this. The filter that is on my 2 HP Johnson is about 3/4 of an inch thick, about 1 1/2 inches in diameter, made with a plastic case. You should be able to find one where they sell lawnmower parts, or parts for small equipment.
Jubilee Clamps are the small metal type that have a worm screw to tighten them. You may also be able to use nylon tie wraps.
You may be able to change the fitting at the gas cap and the Carburator to one that will take the flexible hose and do away with the metal tube altogether.
. I believe the Rubber Type Fuel Hose would be better than the clear plastic, but that is just my opinion.
Hope this is useful to you