The Seachem Bottle Adapter Md for 1 L bottles allows you to seamlessly connect dosing pump tubing to any 1 litter Seachem additives bottles and many other common supplement bottles (with 28 mm opening) on the market. Fits tubing sizes up to OD 0.192 inches/4.88 mm. Simply insert a plug into the bottle neck of your supplement of choice, then insert tubing into its opening. Once inserted, this connection will also help to prevent spillage in the event of a container tipping over. Be certain that the tubing runs to the bottom of the bottle.