Durable, flexible, and easy-to-plumb polyethylene tubing ideal for aquarium reverse osmosis applications. AquaticLife 1/4" Polyethylene Tubing, Yellow is nontoxic and highly resistive to stress cracking from liquid. Use yellow, color-coded tubing to indicate incoming water supply line. Plumb from water supply (standard water faucet or under-sink water line) to the water supply port on your 3-stage reverse osmosis or 4-stage reverse osmosis/deionization unit. 1/4" x 50 ft.