...about two "fuel sender lines" and how I disconnect them (without going under the car):

1) The rubber pump OUTPUT line.
Cut or saw off the rusty hose clamp, use a screwdriver to "assist" the hose off the sender fitting. Refit hose to new fitting. Refasten to new sender with new hose clamp.

2) The rubber covered hard plastic RETURN line.
I have never gone underneath to tangle with the rusty fitting that connects plastic line to (often fragile) metal line.

I use a razor knife to cut off about 2" of outer rubber covering to expose black plastic line. Then I cut the plastic line at end of metal sender barb (I use a small, fine-blade hacksaw.)

Reconnect the cut plastic end to new sender barb with short piece of 5/16" I.D. fuel hose and 2 good hose clamps. NOTE: Return line is low pressure. IMO, FI rated hose is not needed here, standard Fuel Hose is good enough.
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Bruce Young, '93 940-NA (current), 240s (one V8), 140s, 122s, since '63.