Flavor loss is mostly oxidation and moisture pickup. Pre-ground has tons of surface area so giving it fresh air and humidity every day is the main culprit. A one way valve does not address either once the coffee is ground. Choose containers that match your weekly consumption so there is little headspace. Press a piece of clean plastic wrap directly onto the surface before sealing to push out air if your container is a bit large. Store the active container in a steady cool spot away from light. Freeze backup portions in well sealed packs and only thaw them once, while sealed, to dodge condensation.
