Just when I thought I solved the insidious holding tanking tank odor issue . .it surfaced again, I hope only by accident. Over that past weekend I took my 35.5 for its weekly exercise. I know I told the marina to pump the holding tank out during the week as I always do [they said they never got the word] but it wasn't accomplished. While sailing about 15 miles offshore a guest went to use the head. When she pumped the toilet the discharge came out through the holding tank vent indicating a it was full. I leveled the boat out and checked. It was.I tried the macerator but it didn't seem to be doing anything except making a loud noise like a preganat cow. Back at the marina I had the tank pumped [it was full, no surprise] flushed out with water and KO'd. It seemed to solve the discharge overboard problem immediately except for the odor hanging around inside the aft cabin of the boat and on the stren lazarette adjscent to the holding tank. As I mentioned earlier to Peggy, I changed out all the hoses [including the vent] this past spring, cleaned out the tank, checked and rechecked connections and welds . .except for now,the system was odorless. This is the question: Where is the odor coming from? even the bilge smells now but there is no evidence of any leaking waste? How do I get the odor out? - The tank seems to be clean and the dischage hose was also treated. Could the vent hose have gotten stinky from the errant discharge? should it too be flushed out and some KO forced down it? I could probably use a turkey baster from the vent side to do the job. - The macerator makes a very loud noise and does not seem to empty the tank. Maybe I didn't leave it on long enough. It makes a very loud noise. Is that normal? How long should it be on? Any help is appreciated. Fred Miller S/V M Squared