I have had both occurences but for different reasons. The drain blockage in my case was constipation which had flipped the tube up to the top of the abdomen so it couldn't get any fluid out of the peritoneum. The blood was down to adhesions from abdominal surgery which broke apart and then bled into the peritoneal cavity and I am wondering if this maybe a settling down period from the tube being put in which is causing this.
Obviously I don't know exactly what the problem is but the adhesions were not really addressed as they were considered a benign reason and the constipation well I had to have strong laxative medication to make it all shift. Whatever the reason an x ray will at least show if the tube is sitting right and whether there is likely to be something blocking it.
I really hope Ian gets on ok as it sounds like he has had such a rough ride and that he doesn't need any more issues.