There are a couple of different car trailers I borrow from time to time. One has override hydraulic disc brakes. Today it was being used by a 3rd party and the brakes didn't seem to be working. A manual tug (!) and the lever went all the way to market with no pressure. Open cap to reveal the most disgusting mess of contaminated ugly fluid. So a flush and bleed was in order before use. Except one of the calipers is so positioned that you cannot get onto the bleed nipple with a pressure bleeder without removing the wheel. Ok. Into the carport and onto jack stands. Pants off. Both sides. Drained all the old shit and then refill. Flushed about 1L of fluid until it was all nice and clean. Should be no air bubbles. Actually the brakes haven't improved. Careful look under the bed and about 6m of excess brake hose has been coiled up and fixed to the underside about 300mm above the bleed nipples. And even better the hose is coiled through welded on fittings so the only way to remove it is to undo both ends.
I should add even with fucktard design fixed it still took a combo of vacuum and pumping on the lever to shift the air. Lots of air.
Anyway after about 2 hours there are now brakes on the trailer.