Kevin:
You are right about bubbles inside an in-line filter slowing things down. I call that a vapor lock. I don't know if that's truly accurate to call it that. But while using my Platapus Waterworks gravity filter, I learned how to backflush the bubbles out of the filter. The Platapus filter has a little instruction card showing how to do it. You don't even have to know how to read to understand the directions.
KC
Wind in my hair, Sun on my face, I gazed at the wide open spaces, And I was at home.
| 
