I did mine right in the tank, only thing I'm sorry about is I used 1/4" because at the time I was building a return for a carb with a Wix 33040 filter, for vapor lock
I wish now I'd used 3/8 because I've gone to EFI
"WHAT I DID"
Emptied the tank, and cleaned the face off up above the sender.
used an awl to punch and enlarge a hole. Unlike a drill this leaves very little "shavings" and it leaves a nice big edge for silver brazing.
I took my CO2 welding bottle and fed low pressure CO2 into the supply line, forcing CO2 up and out the cap which I removed
Then simply silver brazed a short chunk of tube in there. You can use steel or copper.
You can buy senders with a built in return, don't know what years they fit