Purenex 4.0G Plastic Tank Reverse Osmosis Plastic Storage Tank Only 10" in diameter (takes less space below sink) 100% polypropylene (will not chip, rust or dent) One year limited warranty The following RO storage tank has safe valve with quick connection which is not necessary has to be involved. It is designed to prevent the inside bladder from blowing up. Please connect safe valve with waste outlet or do not connect it at all. It is optional and not necessary.