I recently posted an article about a possible block in my bilge hose. I replaced the siezed pump with the identical model. Although it pumped a little, most of it came back up though the pump and back into the bilge. I removed the hose, the check-valve, ran fish tape, blew air through the hose......no block to be found. The problem turned out to be the new pump ! It has to pump against so much up-hill water resistance, that after a certain pressure built up, water pushed by the joint in the pump where the three pieces assemble. It is designed that way so that it can be removed for cleaning and inspection. By making a o-ring with silicone, the problem was finally solved. In case anyone encounters this problem, the pump is a "Rule- 1000." The schematic for my 1994 C320 shows a "Rule- 800" came with the boat. The previous owner updated it to the more powerful model a few years ago.