Possible Clues:

• Strain
• Color-altering camera lens accessory
• It's a strain to do this
• Purifier
• Abstain from food; not fading
• Spam blocker
• Device for straining impurities from liquid or gas
• Pass through a device to remove unwanted material
• Device for holding back impurities in liquid passed through it
• Device for removing impurities by screening