When we took possession of our boat, it was equipped with two manual toilets with which you pumped the waste into either an on-board holding tank, which periodically had to be pumped out, or overboard. The overboard option for untreated sewage is only legal if you are far enough offshore (3 miles). Both toilets functioned well enough, but much like on our previous boat a smell develops from them if the boat is closed up and left unattended for any period of time longer than a few days. We had done several experiments on our previous boat to try and determine the sources of the smells (it’s not always what you think!) and also did a lot of reading. As you might imagine, there is no shortage of experts on this topic, a sweet smelling boat being a main ingredient of “comfort” while living aboard. The best resource I found online were the writings of Peggy “The Head Mistress”. She adds her commentary to many of the boating Q&A forums we read and is by far the most experienced and logical thinker on this subject. Armed with Peggy’s advice and our own personal experiences with our previous boat, we devised a plan that included four key elements:

Replace all the existing sanitation hoses – while our boat came with reasonably good quality hoses, they were more than ten years old when we started this project and had become one component of the smell problem. In the time since our boat was built there have been several new hose products that have come on the market employing more advanced technology to eliminate odor permeation. The best of these hoses are not cheap and it is tempting to cut costs here. Don’t. As we later found out, you do get what you pay for. We went with the Shields PolyX hose and are very happy we did. Not only have they remained odor free, they are more flexible than traditional wastewater hose which eased the installation a lot.

Re-plumb the toilets to use fresh water, versus sea water, for flushing – this is a controversial subject in many of the boating forums, not because it isn’t an effective odor eliminator, but because some view it as a waste of fresh water. The decision of whether or not to take this step is dependent on a number of variables including available water tankage, time spent at the dock verses on the hook or underway, ability to make water, and tolerance for a small bit of odor always being present. On our previous boat we noticed that when arriving at the boat on a Friday afternoon, after it was closed up all week, there was an obvious smell coming from the toilet. After flushing it a few times the smell mostly went away. The source of this smell, confirmed by Peggy, was actually organisms in the sea water sitting in the hoses and the bottom of the toilet all week, not anything to do with sewage. While there are some mitigations that can be employed to combat this, using fresh water for flushing (just like in a home toilet) instead of seawater absolutely eliminates this source of smell. Given our intended cruising plans and lifestyle while living aboard, plus the fact that we have a large fresh water tank and are now pre-plumbed and pre-wired for a water maker, we were able to rationalize this decision.

Install a sewage treatment system and new electric toilets – An obvious source of sewage smell is carrying around the sewage with you everywhere you go until you come to a working pump out station. We had no choice but to do this on our previous boat because of its smaller size and because we never went offshore beyond the three-mile limit. Our current boat has enough room for a sewage treatment system which obviates the need to carry the sewage around with you except when in a “no discharge zone”. We opted to install the Purasan EX system from Raritan Engineering which is Coast Guard approved and chemically treats the sewage to be far cleaner than the  typical on-land municipal sewage treatment plant. In that respect, it’s better for the environment than using a holding tank since the pumped out sewage simply goes right to the municipal sewage treatment plant. This was simpler to install than you might think (shown below) and has worked extremely well. We also had a decision to make about new toilets. There were three basic choices – manual, electric, vacuum. On our previous boat, I twice had to disassemble parts of the sewage system to free a clog. Nasty, Nasty, Nasty. Oh and one more thing – Nasty! Needless to say, our goal was to minimize the chances of a clog as much as possible. We liked the idea of an electric toilet since the first thing it does in the flush cycle is grind up the waste before it even enters the discharge hose. In addition, the configuration of the grinders creates a pumping effect which forces the ground-up waste through the hose. Because of that, a smaller diameter discharge hose can be used which has the added benefit of having a smaller surface area for odors to emanate from if the hose has any permeability to it. The Purasan unit receives the ground-up toilet discharge and then subjects it to two additional grinding cycles of its own along with the chemical treatment. All that happens before the sewage is forced through a long length of hose to a vented loop prior to going overboard. We’ve had this in operation for over three years now without any clogs.

Improve the air ventilation to/from the holding tank – With our holding tank remaining empty most of the time now, it is no longer a contributing source of smell. However, when it is used (in no discharge zones) it is critical that there is enough air flow from its vent to the outside to mitigate any smell from the tank on the inside of the boat. The existing vent hose and connectors on our holding tank were wholly inadequate for this. We doubled the size of the vent hose and replaced the connectors at both ends with much larger ones to greatly increase the air flow.

Below is a picture essay showing how all these improvements were done for the forward head. The aft head was actually a lot easier to do because the hose runs were not as complicated and the work space under the floor was easier to negotiate.