PS Advisor January 15, 2004 Issue

PS Advisor: 01/15/04

Holding Tank Refits
We own a Com-Pac 25 and we enjoy making improvements to her.  Now I'd like to replace all the flexible hose plumbing in the head compartment with PVC, hoping that'll eliminate the odor problems we occasionally have. Also, the holding tank, which is located under the port settee, just aft of the head, is too small, but it probably couldn't be replaced with a larger one because of the size of the access hatch. I wonder if the whole compartment it sits in could be turned into a permanent built-in holding tank enclosed by the hull and quarter berth with added fiberglass to form the two ends and the top.  Is this ever done? 

Would the inside have to be lined with any special material? I have a feeling there's a good reason not to do this.  Can you advise?

-Michael Hoffman
Concord, MA 01742

On matters of marine sanitation, it's always best to secure the advice of Peggie Hall, a specialist in marine sanitation for many years, and known in some circles as "The Headmistress." Here's her response:

"Using PVC pipe isn't a great idea on a boat that size. Hard PVC is only recommended for use in a long, straight run. Short runs with any bends require the use of many inline radius fittings that must be cemented, creating the potential for leaks and a lot of 'bumps' in the line where waste can become trapped and build up. It's also necessary to soft-couple hard pipe to anything rigid—toilet, tank, through-hull, etc—with enough hose to absorb shock and allow for flex.

"If the odor is only in the head, and is only occasional, the hose probably isn't even the culprit. It's more likely to be stagnant seawater trapped in the head intake. That's definitely the case if you only have odor when you flush the first time after the boat has been sitting for a while.

"If the odor is constant and strongest in the areas the hoses pass through, then replacing the hoses should cure which case, I recommend using SeaLand 'OdorSafe' brand hose. It's expensive, but the only hose that really is just about bulletproof against odor permeation.

"I wouldn't turn a locker into a holding tank, for several reasons. First, once you do it, that locker will be a holding tank forever, because you'll never get the odor out of it. You may not ever want to convert it back to storage, but the next owner of your boat may have other ideas. Second, sealing up an area that was never meant to be watertight is likely to be difficult, because boats flex. Third, any problems that can develop due to water intrusion into a fiberglass hull—blisters, cracks in the gelcoat, and/or epoxy coating, etc—are even more likely to occur inside a tank...and because they're occurring inside the tank—especially a waste tank—they won't be noticed until the damage becomes extensive.

"There’s a very simple solution to the problem: Enlarge the hatch enough to put a larger tank into that space. If necessary, open up the top of the compartment completely and replace the material removed with a sheet of plywood that can easily be removed whenever necessary.

"As for a source of a tank to fit—or at least maximize—that space, I recommend Ronco Plastics. They make excellent tanks for a very reasonable price, and have more than 400 shapes and sizes to choose from—over 100 of which are non-rectangular. And they install fittings in the sizes and locations specified by the customer when they make the tank."

Peggie Hall's book, Get Rid of Boat Odors—A Guide To Marine Sanitation Systems and Other Sources of Aggravation and Odor, is available directly from her publisher, Seaworthy Books (

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