You can use a filter 0.2 µm for plastic syringe next to a flame or under biosafety hood or under laminar flow hood to avoid contamination to filter your buffer containing 8-10% sucrose in a pre-sterilised bottle.
Don't forget to always be in the sterilse zone (when you use a flame) when you open your bottle and when you filter your buffer directly in the sterile bottle. Try to don't manipulate the filter and syringe where you plug them together. For the syringe, manipulate it from the top near the piston. For the filter, open it without touching it and plug it right aways in the syringe.
I'm sorry if I wrote many details, I just want you to manipulate it the most strelise way to avoid contamination!