From the freshwater supply to fuel and wastewater, knowing the level of all tanks is essential for comfortable and safe sailing. Several tank-monitor manufacturers now refer to three types of tanks: fresh for drinkable water, gray for drain water from sinks and showers, and black for wastewater holding tanks from toilets. Its the black water were concerned about here.
Whether youre starting out on a Sunday daysail or a two-week inland cruise, one of your checklist items should always be Check the tanks-especially the holding tank. Knowing the holding tank level does more than help you avoid an uncomfortable situation when a guest goes to pump the head. It can keep you from running afoul of the law.
Federal law mandates that all boats with permanent toilets have either an on-board treatment system or a holding tank to store wastewater. Many states have inland lakes and coastal areas that are designated as No Discharge Zones (NDZ), areas that prohibit discharge of untreated waste into the water. Unless you are far offshore or in coastal waters where direct discharge is legal, suddenly discovering the holding tank is full is surefire way to ruin a sail.
Most older and smaller boats do not have level gauges on any tanks. A captain just knew about how full his tanks were or could judge the level by simply thumping the tank with his knuckles. Occasionally, if the tanks had inspection ports, a visual check with a flashlight or inserting a dipstick was sufficient.
Today, there are several options for measuring tank levels, starting with the simple internal float gauge and progressing to sophisticated ultrasonic capacitance or sonar internal probes. Not all holding tank gauges work as well as they claim-and when they fail, the consequences arent pretty. Fortunately, Practical Sailor has just wrapped up extensive testing of marine plumbing components. Weve picked the winners and losers in each category, including holding tank sensor, and offer tips on installation and maintenance.
For a complete review of holding tanks and the gauges and sensors available to measure their levels, purchase and download the Practical Sailor ebook, Plumbing and Odor Control.
