Pressure transfer

I’m thinking with the right mix of hobbled fittings I could pressure transfer from a bucket to keg. Anyone have any valid reasons I couldn’t?

No reason you can’t. I’ve seen several creative ideas that work.

Nope.  But you could also start a siphon into keg and once siphon is going direct the CO2 exiting the keg into the bucket to achieve a nearly closed transfer.

Yep, I close loop transfer a lot (mostly with my 10 gallon lagers, but also with ales that are in the right fermenter).  I mounted a cornie “gas in” keg post on the top lid of many fermenters, so I first fill the keg with sanitizer, proceed to purge receiving kegs with CO2 pushing out all sanitizer, then I use the CO2 pressure in the keg to purge the receiving line and CO2 line, then I hook up a receiving line from the fermenter spigot to the keg out post and a CO2 line from the keg in post to the fermenter lid in post.  I can also pressurize the fermenter slightly by first hooking up a CO2 tank line to the fermenter lid, if I want to transfer the fermented beer at a quicker rate if I need to do that, but I rarely find the need to go that route.

I use the fermenter lid posts as blow off tubes during fermentation (I typically use 7 gallon SS Brew Tech fermenters for ales and 14 gallon Chapman SS fermenters for lagers).

Just one way to do it.

Cheers.