A flow controller having an internal tubing is provided. The flow controller may include an upper housing having a plurality of graduations, a lower housing engaged with and slidably coupled to the lower housing, and a cavity defined between the upper and lower housings for accommodating at least a portion of internal tubing. The flow controller may further include a flexible clamp having an upper section mounted in the upper housing and a lower section slidably disposed in the lower housing. The upper and lower housings may be slidably coupled relative to each other to transition the internal tubing from (i) an open position where a lumen of the internal tubing is uncompressed by the flexible clamp to (ii) a closed position where the lumen of the tubing is at least partially constricted by the flexible clamp.