open up a bleed nipple n pump till no more fluid comes out...

ths will clear out 90% of the fluid. so when you now remove your brake line from the master cyl only a little bit will dribble out

then remove master cyl (keep rag around the thing, dont want any spillages!) refit, do up the lines, refill... bleed brakes, n jobs a goodun

did mine by myself using 1man bleeding tool n job took approx 1hr start to finish using shit tools...

the cyl change itself took about 5-10mins