A reservoir is not decoration; it is the point where the loop breathes. Taller than it is wide, the 120 mm glass cylinder keeps a steady head of coolant above the pump inlet, so air collects in one visible place instead of cycling through the blocks. A fill port sits on the top cap and a drain valve on the bottom, which turns a full teardown into a five-minute job.The glass is annealed slowly after forming, which is what lets a wall this thin hold pressure without the micro-bubbles that cloud a cheaper tube. Both end caps are cut from solid aluminium on the same CNC bench as our waterblocks, then finished by hand. Filled to the 300 ml mark, the cylinder shows coolant level from across the room — a useful habit on a loop you plan to run for years.