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If your boat has a head, regular maintenance of the blackwater tank is critical for reducing buildup, deposits, and odors. Here are some options
Giving your holding tank a deep cleaning and flush a couple times a year will help keep it working properly and reduce odors. Photo: Brian Mistrot
Hang around boats long enough and you’ll inevitably hear someone mention the need to “shock” their holding tank. You’ll likely find it an odd statement, while simultaneously thinking, “Does my holding tank require a shocking as well?” Here’s the lowdown on how to properly clean your holding tank and avoid all this “electrifying” talk.
The word “shock” is likely a reference to the practice of shocking a swimming pool by adding extra chemicals to oxidize and sanitize the water. To boat owners, “shocking a holding tank” means adding copious amounts of some chemical with the hopes of neutralizing odor, while at the same time magically dissolving any poo-induced buildup.
Taken in this context, “shock” is not really the best choice of words when it comes to holding tanks. Cleaning the holding tank is more accurate, as the ultimate goal is to facilitate a more thorough cleansing of the tank at pumpout, rather than to deodorize its contents. This is particularly true with regard to buildup and deposits.
It’s also important to differentiate between shocking a tank and managing it by regularly adding small amounts of chemicals to help with odor control and promote a “healthier” holding tank environment.
It’s in there
Solid waste is comprised primarily of water, meaning it will readily dissolve in the water of your holding tank. Most holding tank buildup comes from toilet paper or (if saltwater is used for flushing) calcium carbonate scale, which is produced when uric acid (in urine) mixes with saltwater.
If this buildup is still soft or spongy, then shocking the tank in preparation for cleaning will offer a much better chance of success. If the buildup is solidified or completely hard, shocking the tank may be of some benefit, however, the only real options at that point are to either live with the buildup, manually clean the holding tank, or (in extreme cases) replace it.
Best cleaning practices
When it comes to reducing holding tank scale and buildup, the best practice is to treat and clean the tank regularly to avoid accumulation in the first place.
I like to deep clean my boat’s holding tank at least twice a year, one of which typically coincides with fall layup if the boat will be winterized. My deep-cleaning process is as follows. I’ve found it works well for a midsize holding tank of around 20 gallons but can be modified as needed for larger or smaller capacity tanks.
1. Pump the holding tank.
2. Mix 2 cups of Calgon Water Softener in 1 gallon of hot water, then pump into the tank.
3. Add 1 cup of biodegradable, bleach-free liquid laundry detergent to 1 gallon of hot water, then pump into the tank.
4. Let sit for several hours or overnight.
5. Top off the tank with freshwater, let sit for a couple of hours, then pump out the tank.
6. Using the pumpout station’s hose, fill the holding tank with freshwater right after the pumpout, and then immediately pump that out. It’s even better if you can repeat this step a couple times.
Only use chemicals made specifically for the materials used to construct your boat’s holding tank. Photo: Frank Lanier
Flush or toss?
Many people swear by (or at) not putting toilet paper into the tank, living by the well-worn creed of “nothing goes in the toilet that hasn’t passed through your body.” Some try to mitigate the issue by purchasing toilet paper specifically designed for use in marine heads and holding tanks, but I’ve never seen any definitive proof that its use makes any difference. Therefore, I suggest keeping a small, lined trash bin with lid in the head, and instruct your crew members and guests to toss all paper. — F.L.
Shocking the tank
If you want to shock the tank using chemicals, that’s easy and straightforward as well. Simply purchase one of the many holding tank shock treatments available on the market, add it to the holding tank per the manufacturer’s instructions, and let it slosh around for three or four days to a week (depending on manufacturer directions). Then pump out as normal.
If you’re doing this as part of your winterization process, I like to put it in the holding tank about a week prior to the final pumpout of the season, which gives it plenty of time to slosh around.
If you’re heading out for a final day on the water before winterization, add a couple of buckets of ice to the holding tank (via the access port) after shocking, and let it scour the tank during the trip. Once back at the dock, pump out the tank and do a final rinse with fresh water (fill the holding tank about half-full), then pump that out as well.
This not only helps with scale buildup but also ensures a clean last pumpout of the season prior to storage.
Never shock your tank using chemicals not specifically designed for it – such as residential toilet drain cleaners or decloggers. You also need to know the material your holding tank is constructed from and choose compatible shock treatment chemicals to avoid adverse reactions and damage to the tank.
The manual cleaning option
While not the easiest or most enjoyable option, manually cleaning the holding tank does provide verifiable (if odiferous) results. If it’s an option (which will be based on your location), clean your holding tank during cold weather to help keep down the smell.
While the specific cleaning steps will be determined by your particular installation, the basic steps are to empty the holding tank, flush it with fresh water, remove the tank access plate(s), then clean by spraying the inside with a high-pressure hose. After accessing the tank, you can also spray a suitable cleaner inside and let it sit awhile prior to spraying with the hose. A disposable stick will help to dislodge stubborn areas of residue.
Manually cleaning a holding tank is a nasty job, so in addition to keeping your mouth closed while the action is going on, do yourself a favor and follow these other cleaning tips:
- Provide adequate ventilation. If possible, clean your tank outside.
- Wear appropriate protective equipment such as a raincoat, rubber gloves, and goggles or (preferably) a face shield.
- Follow the manufacturer’s guidelines for using tools and/or chemicals.
- Be aware of what you’re doing and use common sense!