hi!

usually use marshy brake bleeding method, works great on my saints, for example

struggling with an xt rear brake, have just zip tied lever to bar and will leave overnight. never tried it before. will it work?

Assuming good routing, and lever higher than caliper, gravity (air being lighter than brake fluid) should allow air to rise to the lever (reservoir) overnight while tied but it won’t remove the air from the system.
bleed the lever in the morning for that.
tieing your lever to the bar also won’t ensure there’s no air stuck in an awkward place somewhere within the system. also the firm lever feel won’t last if you have the shimano patented weaping caliper seal feature.
it’s a lazy bastard fix. so worth trying IMO.

what’s the marshy method?

I’ve used the zip tie method on SLX and Deore with some success.