What minimum volume of water should be used to flush an NG or PEG tube before and after administering Dexsol 2 mg/5 ml oral solution?

For Dexsol 2 mg/5 ml oral solution, use only unobstructed silicone, PVC or polyurethane NG or PEG tubes and flush with at least 5 ml of water before and again after dosing; use only water flushing because air flushing risks underdosing by up to 50%.