to rotate relative to the mount 14 to position end 29 at the required level within the reservoir 50 the tap 27 is moved to its open position this allows fluid to flow from the container 11 through passage 31 and into the reservoir the tube 32 and passage 30 allows air to enter the container 11 to prevent the formation of a partial vacuum in the container 11 the formation of a partial vacuum has the tendency to form a vacuum lock which inhibits or prevents fluid from flowing from the container 11 when the reservoir 50 is filled up to a level dictated by end 29 of the stem 13 ends of the passages 30 31 are immersed in fluid 51 at which time no further fluid 52 is able to flow through passage 31 and no air is able to flow through passage 30 the brake bleeding operation may then commence as fluid 51 is drained from the reservoir 50 more fluid 52 is able to flow into the reservoir and air may flow into the container to prevent formation of a partial vacuum in the container 11 once the bleeding operation is complete tap 27 is turned to its u201c off u201d position and the apparatus is unclamped from the neck 53 of the reservoir 50 this is a one handed operation the spring based clamping action securely locks the apparatus relative to the neck of the reservoir the adjustment of the position of end 29 within the reservoir to control the level of fluid within the reservoir is a one handed operation and simply requires.