have a bucket of clean soapy water at hand then remove the cap and loosen the bleed nipple (just enough for the fluid to drain slowly)
let gravity do the job
as the dirty fluid drains out, top up the master with new , swill the dirty fluid away so as not to affect any surfaces
when you see clean fluid draining nip up the bleed nipple and ensure there is enough fluid in the master .
wash away any fluid .
work the clutch a few times and you are ready to go