I've got a 4L gravity filter from Platypus. It's about 5 years old. I filter about 50 gallons/year but haven't good about regular back-flushing of the filter. I have a syringe from my Sawyer mini. Can I use that to backflush the Platypus filter? And if so, better to backflush gently or go ahead and give it a good spray thru?