I did some digging today before I found this and decided to take my B150 (commercial brewer) apart to blow compressed air up the exit tube to "clear" it. Well, these big machines are not that simple. I ended up right by the needle and found the backflow preventer. I decided to just remove it to see if it improved flow. Well, it did! I never saw grounds in it and it takes a bit of flow to open the valve. I will monitor it to see if this is true issue or not. If it works for the next week, I will hunt for a new valve, or just omit it?