Written by Dave Dave
Published: 20 April 2017 20 April 2017
Last Updated: 28 September 2017 28 September 2017
Hits: 2764 2764

Sleeping soundly on Identity Crisis, our 1981 Sabre 30 was becoming a challenge. The cushions were fine, the docks and anchorages secure. The company could not have been better. It was the odors wafting from the holding tank and plumbing located beneath the V-berth. It was clearly time to upgrade the plumbing.

Causes of head odor

The first step on the way to removing the odor was to understand the cause of the odor. Peggie Hall’s book Get Rid of Boat Odors was a helpful resource. The root of all head odors is the bacterial process by which waste decomposes. Head odors are the result of the good guys losing to the bad guys.

The good guys are the aerobic bacteria; naturally present in waste they produce odorless carbon dioxide (CO2) as they breakdown solids and paper in the wastewater. Aerobic bacteria need lots of oxygen to thrive, thus, given a consistent and large enough supply of oxygen, there would be no odor from the holding tank.

Anaerobic bacteria are the bad guys. These bacteria thrive in the absence of air and produce sulfide gases, which smell bad. Anaerobic bacteria also produce methane and CO2, However, most holding tanks do not have sufficient ventilation and since CO2 is heavier than air the CO2 settles on top of the waste and chokes the aerobic bacteria while providing a prime environment for the anaerobic bacteria.

This process can occur any where standing sewage is standing, on Identity Crisis the possible culprits included the holding tank and the hoses.

Locating Odor Source

Armed with the knowledge of how the head odor is created, I began an investigation into the source. The first and primary suspect was the hose itself. When waste lies in a hose, the odors caused by the anaerobic bacteria will eventually permeate the hose. Placing a damp cloth on the suspect hose for a few hours will cause the cloth to absorb some of the odor confirming that the hose has been permeated. Visual inspection of the hose, showed it was original equipment and 27 years old, far past its prime.

Problem one: old smelly hose. It had to go. On a cool fall day with the boat on the hard, the hose made a quick trip to the dumpster.

The next suspect was the holding tank itself. Using a wet rag, I determined that the odor had not permeated the tank walls. However, with the inspection port open and the hoses removed, there was some odor being emitted from the inside of the tank, but not enough to warrant the cost of replacing the tank.

Inspection of the plumbing system revealed several additional concerns. First, the hose runs appeared unnecessarily long, the discharge hose would always have waste in it, and the hoses sagged in several places providing the perfect places to trap waste and generate odor. A redesign was in order. The primary objectives were to reduce the plumbing runs and eliminate standing waste in the hoses.

Reducing the hose lengths had two benefits. First, at $8.OO per foot, saving a few feet of hose would have a positive effect on project costs. Second, by reducing the length of the intake the size of the holding tank would be effectively increased. Each foot of 1.5 inch hose holds about 12 oz. By reducing the hose run from about ten feet to three feet the amount of water required to flush the hose clear of any waste would be reduced by three quarts. In a 22-gallon holding tank, that’s a sizable amount.

Rigid PVC pipe is impervious to odors and is now commonly used in home and commercial plumbing. It appeared to be the obvious choice to replace any hose which was subject to standing waste water, in particular the tank discharge line. The problem was how to relocate the fittings. The solution: an innovative product from Austrialia, the Uniseal ( The Uniseal would allow both the intake and discharge lines to enter the tank from the top eliminating standing waste in the hoses and shortening the hose runs.

The Uniseal is an inexpensive rubber grommet that allows pipes to be inserted in to tanks. Installation is simple, drill an appropriate sized hole in the tank, insert the Uniseal and then lubricate and insert the PVC pipe.

Installing the fittings

The original tank fittings had the discharge line leave the tank at the bottom of the tank at the aft end and the intake line at the top of the forward tank wall. Both fittings were 1.5 inch male to hose fittings that unscrewed from the tank. Standard 1.5-inch PVC plugs were screwed into the tank fittings to seal the holes. Because of the short thread depth on the tank it is important to not over tighten the plugs or the plugs will leak. Place a couple of wraps of Teflon pipe tape on the threads and screw in finger tight, then turn the plug about a quarter turn with a pipe wrench and stop.

Next locate the intake fitting. The location is not particularly critical; it should allow for a downhill run from the Y-valve and be in an accessible place. Use an appropriately sized hole saw to make the hole. (Use the recommended size provided by It is best to use a new sharp hole saw. Dull saws may overheat and cause the plastic to melt. Use a piece of 150 grit sand paper clean up the edges of the hole so that they are smooth, without jagged edges or burrs. The Uniseal will pop right into the hole.

The fittings consist of three parts, a 1.5 inch male by hose barb fitting (Available from Defender), a 1.5 inch female by slip PVC elbow (available at hardware stores), and a section of PVC pipe. Screw the hose fitting into the elbow after wrapping the threads with Teflon tape and glue the elbow on the section of pipe. The length of the pipe on the intake fitting is not critical; it only needs to protrude through the fitting by an inch or two. I used a 5-inch piece. Lubricate the pipe with regular dishwashing soap and insert the pipe through the Uniseal. The pipe will slip easily through the seal and once the soap dries it will be difficult to move, so be certain to properly align the elbow. Finally attach the hose with double clamps.

Moving the discharge hose from the bottom of the tank to the top requires installation of a standpipe. Greater care must be taken with locating the standpipe than the intake hose. In order to be effective, it must be located directly over the lowest spot of the tank and reach the bottom of the tank.

Building the standpipe is straightforward. Begin with length of 1.5 inch PVC that is several inches longer than the depth of the tank. At one end cut a section of the pipe off at approximately a 30 degree angle leaving about half the pipe the original length. Clean the cut edge with sandpaper to remove burrs and reduce the chance that solids will get caught on a rough edge. We are trying to create a door into the standpipe. When installed, it must touch the bottom of the tank and have a opening for the waste to enter. Insert the pipe in the hole before installing the Uniseal. Mark the pipe at the point it exits the tank and remove from the tank.

Before cutting the pipe to length, add a few inches to accommodate the thickness of the Uniseal and the length necessary to attach the elbow. Cut the pipe and attach the elbow and hose adapter. Install the Uniseal, lubricate the standpipe and insert, taking care to aim the elbow in the correct direction. The standpipe should be seated against the bottom of the tank and the opening oriented towards the middle of the tank. Finish by connecting the discharge hose.

Final Testing

Before placing the holding tank in use, it is wise to check for leaks. Place a paper towel under the now plugged old discharge outlet, the intake hose fitting, and the discharge hose fitting. Pump water through the head and into the tank, it will easier to detect small leaks on the paper towel. Finish filling the tank with freshwater and add a couple of gallons of white vinegar and go sailing. The vinegar will help freshen the tank while sailing with a full tank will put enough hydrostatic pressure on the fittings to reveal any leaks. After a couple of days, if leaks are absent, pump the tank and enjoy a good night’s sleep.

Potential Problems

The most serious potential problem is a leak at the old discharge fitting. If the new plug leaks, remove it and try using a heavy “natural gas” Teflon tape. This tape comes in a yellow container, is thicker, and costs a bit more than standard Teflon pipe tape. Second, make certain that plug is appropriately tightened. Too loose, it will leak; too tight; it will leak. Best to check this with fresh water.

A second problem that could occur is with the standpipe. If the opening is too small or too close to a side wall, the flow could be restricted when pumping out. Thoughtful prior planning will prevent this from occurring. There will always be a small amount of liquid that can not be pumped out, even with a bottom discharge. If the standpipe does not reach the bottom of the tank or if the opening is too large, larger amounts of liquid will be left in the tank.

Strategies to reduce Odor

According to Peggie Hall, there several strategies can be employed to reduce odor. First and foremost is to increase ventilation. Ideally, the tank should be cross-ventilated with adequately sized hose, at least ¾ inch diameter. The vent lines are installed in the same manner as the intake line and vented outside.

Flush the line from the head to the holding tank with enough water to ensure the hose is free of waste. With shorter hoses and better gravity feed from the hose, less water is needed to rinse the hose. This translates to less frequent pump-outs.

Finally, avoid placing chemicals in the holding tank. These chemicals and common household cleaning agents will kill the aerobic bacteria, the ones necessary for odor free waste decomposition. Raritan markets products that are safe for the holding tank and promote aerobic bacteria.


Author’s Note: The author is appreciative of the discussion and comments on the Sabre email group on this issue and especially those of Peggie Hall who provided expert guidance on the design.

Parts List:



Approximate Cost

Trident 101 Sanitation Hose

$8.00 per foot

2 1.5 inch Uniseals

Aussie Globe

$10 including shipping

2 1.5 inch male by barbed hose connectors

$2.50 each

2 1.5 inch PVC elbows female by slip

Local Home Improvement Store

$1.32 each

3 feet (approximate) 1.5 inch PVC pipe

Local Home Improvement Store


4 SS hose clamps

Local Home Improvement Store


Teflon pipe tape

Local Home Improvement Store


PVC Cleaner and Cement

Local Home Improvement Store


Approximate Total Cost (excluding hose)