Big syringe is the easiest , go to a rural supplies place or a vet and tell them what you're doing and you want a good sized one . It will be pretty much a single use thing though but should last the day out , brake fluid does horrible things to a lot of syringes .... Either that or I have a sludge pump from supercheap , like a metal syringe about 10 inches long and 3 inches diameter , pull the handle back and it sucks up the fluid , probably best to get one just for brake fluid and not use it for other things if you want to keep the fluid clean for topping up afterwards (but better to throw it out anyway and use fresh stuff to top up with ....) . It's a handy gadget for other things too (draining a bit of excess oil after someones overenthusiastically filled the oil
) but attach the rubber hose to the end with a good hoseclamp so it doesn't fall off into the sump ...