In between the extremes of ignoring the cylinders and draining every last messy drop is to drain the bulk of the fluid in the cylinders.
Remove the bucket. Fully extend the pistons -- ie: arms in full raise, bucket mount fully dumped. Shut down the tractor and drain the sump, etc. Move the lever to the full curl position and secure then manually move the bucket mount to fully retract the cylinder(s). That will force the oil out of the cylinder back to the sump, drawing mostly air into the opposite end of the cylinder. You can move it back and forth a couple of times to try and pump as much as possible out, changing the lever position each time of course. (If your dump spool valve has a "regen" position, avoid moving the lever that far. No point in cycling fluid back and forth).
Once the bucket cylinders have been emptied, move the lever to lower the arms, letting gravity push the fluid out of the lift cylinders. Repeating this one up and down is probably less of an option due to the weight of the arms, but hey, if you have things positioned under some chainfalls in the garage or under a tree: have at it.
There will still be some residual traces of fluid in the lines, but you will have removed most of the fluid from the system.
Edit: don't forget to leave the 3ph lift cylinder fully down.