The pressure fuel line with the fuel filter goes to the bottom of the carburetor while the fuel line without the filter goes to the top of the carburetor.
If you're replacing fuel line on a weed eater or chainsaw.
The (clear) main fuel line with the filter (filter inside the fuel tank) goes to the bottom of the carburetor (or the elbow shaped nipple).
The (clear) fuel intake line runs from the top of the carburetor (straight nipple) and goes to the short post on the back of the primer bulb.
For fuel line you need tubing that can withstand fuel as well as pressure.
Stainless steel, rubber and even polyurethane are common tubing types for fuel line as well as steel tubing.
You can use rubber hose for fuel return line as long as it's rated for fuel.
It is OK to use rubber fuel lines for fuel as long as the rubber hose is rated for fuel such as gasoline and diesel.
The size that most fuel lines are would be 3/8 inch size.
The most popular fuel line sizes are.
-6AN (=3/8" OD)
-8AN (=1/2" OD)
-10AN (=5/8" OD)
-12AN (=3/4" OD)
You can use braided hose for fuel line as long as it's automotive type braided hose and rated for fuel.
You cannot use braided hose that is rated for water or non fuel as it can degrade and leak.
But use of braided hose such as stainless steel braided automotive fuel line is good and can be used for fuel including gasoline.
Polyurethane tubing can be used as fuel line as polyurethane is resistant to gasoline, diesel and most other fuels and chemicals which make it an ideal tubing type for fuel lines.
Vinyl hose will not work on fuel lines as vinyl cannot withstand the contact with fuel and will degrade and leak.
Also gasoline and other fuel tends to make a clear vinyl hose go hard, and when that happens the pipe may become brittle and the seals at each end may be compromised.
Silicone tubing and hoses are not resistant to gasoline as silicone hoses are porous and not suitable for fuel or oil.
Stainless steel can be used for fuel line as it's resistant to fuel and good for high pressure as well.
The best material for fuel line is braided stainless steel fuel line that has much higher heat resistance and withstands high pressure liquid better than other fuel hose.
Rubber fuel hose is also good for fuel line.
Fuel lines don't usually need Teflon tape if you're using compression fittings.
However some fuel lines may need Teflon tape depending on the type of fuel line connector you're using.
You can Zip tie fuel lines to hang them or to also submerge the fuel hose in gasoline or diesel.
Plastic zip ties are fuel resistant and safe to be submerged in fuel.
Nylon fuel zip ties are also fuel resistant and also resistant to most chemicals.
The hose clamps for fuel line should be tight enough so that it's squeezes the fuel line somewhat and tight enough so the hose cannot be pulled off.
Tighten the hose clamp a little at a time and check the hose.
Just make sure the fuel hose clamp is not tight enough to cut into the hose.
You can use polyurethane tubing as fuel line as it has exceptional resistance to most gasoline, oils, kerosene, and other petroleum-based chemicals, making PU tubing and hose an ideal choice for fuel lines (although additives in today's gasoline and petroleum products warrant field testing).
The kind of hose you can use for fuel line is rubber fuel line hose that is rated for fuel.
SAE 30R7 hoses are designed for fuel.
Rubber hose that is rated for fuel can be used for return fuel line as well as pressure fuel line.
When using rubber hose for fuel line pressure make sure the rubber hose is rated for the fuel under pressure.
However any fuel hose that is rubber will be okay for fuel return line.
However just note that regular non fuel rated rubber vacuum or heater hose should never be used in fuel applications.
The hose will deteriorate from the inside out and can plug fuel filters and carburetors with rubber debris, long before it springs an external leak.
SAE 30R7 hoses are designed for fuel.
These can go under the hood and are typically used for low-pressure applications like carburetors or a fuel return line.
It can also be used for PCV connections and emissions devices.
SAE 30R9 hoses are designed for high-pressure applications like fuel injection systems.