Google is your friend........Atrium Medical: Ocean™ Wet Suction Water Seal Chest Drain
means that you can measure two separate chest tubes into one container.....they are made for this each cheat tube goes to it's own connector on the drainage unit itself.
Many times two chest tubes will connect to a y connector to a single tube that connect to the unit.
To change a unit....first call the MD to ensure you may clamp the chest tubes to change the unit. All your questions are answered at the website I gave you.