Peggy - When my first mate was pumping the head, the cabin filled with a strong odor from the holding tank.... but she didn't smell it in the head! We didn't have enough time on the boat to diagnose this before we left, but I'm guessing it is likely to be a detached vent line at the holding tank. We tried it twice and got the same results - main cabin stinks, but not the head! Any other possible diagnoses? Thanks! Michael O'