I'm using the pipe attachment and when i press Alt + click to transfer fuel, the fuel transfer buttons don't show. I'm using KSP 1.2.2, 64x version and my KAS version is "VERSION": {
"BUILD": 0,
"MAJOR": 0,
"MINOR": 6,
"PATCH": 2
} (from the .version file)

Have you enabled option "Resource Transfer Obeys Fuel Crossfeed" in game settings? If yes then it's not going to work. See #189.

I would actually suggest an enhancement on that note: is it possible that the pipes work as real KSP pipes so that they work even when "ObeyCrossfeed rule" is enabled? I will open an enhancement suggestion to make this suggestion easier to track. Thank you.