Secluff has given a very thorough answer and explanation in his post above. I like the photos provided and plan to snag them to enhance my current documentation. The Fuel Evaporative System is one of the more misunderstood emission control systems. Like the PCV Valve, a lot of folks end up disabling it not realizing how beneficial it is when it comes to all but eliminating the smell of fuel vapors in a garage (and reducing unburned hydrocarbons into the atmosphere). It does nothing detrimental to engine performance, not one bit.
Not only have I see folks bypass it, I have seen a few situations where the canister's outplet port that is supposed to be connected to the steel tubing going bacl to the fuel tank's liquid/capor separator valve is connected to the intake manifold. Not only is that an incorrect connection, it ends up applying engine vacuum to the fuel take, that causing a real battle for the fuel pump to overcome when vacuum is applied to the fuel tank while the pump is fighting hard to pull liquid gasoline out for delivery to the carburetor. Unless someone put a vented fuel cap on the fuel tank it can cause some real unusual fuel starvation issues.
Attached is the 1973 emission control info from the Shop Manual Volume 6 excerpt. It covers how the fuel evaporative system is designed, has some useful diagrams, and also include vacuum routing for 1973 Mustag/Cougar emission control systems. A lot of the emission control system info is similar, or in some cases the same, for the 71 & 72 Mustangs, although the Exhaust Gas Recirculation (EGR) system was introduced in 1973, for 72 and earlier engines you can ignore the EGR related systems documented for 1973 engine calibrations.
I also took some photos of the Fuel Evap system line connections that I think might be of help in addition to the nice photos Secluff provided. The files I have are on my Google Drive at the following location:
https://drive.google.com/drive/folders/1EVTRcv1bfvPPF8HXYk-2S0evxgUSBGYM?usp=drive_link
I also have (of course) a YouTube video I made showing out 1973 Mustang's Fuel Evap system at:
I will be adding Secluff's photos to my files later this morning, giving him credit for the photos of course (many thanks, Secluff).