Have a machine with the drain board constantly backing up. Took it apart and found no obtstructions and hoses are free of build-up. Any suggestions?

My suggestion would be to switch over to priming buckets. But we know that they will not want to switch back. I would have them pull the machine. Once it is in your possession, I would put the drain line in a five gallon bucket, and pour water down the drain. That will isolate the drain board and you can rule out the drain line. Secondly I have seen cath caps and saline caps get stuck in the drain boards before. I would completely disassemble the board after you rule out the drain it self. The blue cath caps are sometimes hard to see especially when you are in a hurry and do not have a lot of time to look between patients. Let us know,