Hmmm, don't know. What size syringe are you using. If you are using a 20cc syringe, go to a 5cc syringe. The lower the volume syringe, the greater pressure that can be applied.
Also, pre-filtering is not totally necessary. I filter all my stuff at least twice, but if you get some binders and glue in your final mix, it won't really affect you at all.