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Pump Outs: The Scoop On Poop!

You might want to ignore everything associated with pumping out, but you shouldn't. Here's how to properly use a holding tank and onshore pumpout station.

The — ahem — business end of your marine head is only the beginning of what you need to think about after you flush, when waste typically travels to your boat's holding tank. While there are a variety of options for onboard waste management, ranging from chemical toilets and composting heads to full-onboard treatment devices, the vast majority of boats have a simple marine head connected to a holding tank. Regular pumpouts are a good idea to ensure that your holding tank always has room when you need it. Knowing the location of the closest pumpout station is also a good habit.

Pumping out at the holding tank

Photo: Brian Mistrot

A typical Type III marine sanitation device system (see illustration below) consists of a holding tank fitted with a head-discharge hose, a pumpout hose, and a vent line. In addition, some systems include a macerator to chop the waste up into disposable small bits. The discharge hose feeds the tank from the head and empties into the top of the tank. The pumpout hose allows you to use a pumpout facility, pulls from the bottom of the tank, and leads to a through-deck fitting. The vent line, which is a smaller-diameter hose, allows air into the tank for the aerobic breakdown of wastes and to replace the wastewater volume when it's pumped out.

How To Pump Out

Topside, you'll find a waste fitting to which your pumpout hose connects. Most of these are sealed with keyed plates, requiring a special tool to open. Put on gloves. You can buy inexpensive disposable nitrile or latex gloves in bulk at West Marine, Home Depot, or online. Spin the waste fitting cap off and set it aside where it won't slide overboard. Read the instructions on the pump. Next, make sure the valve on the nozzle for the shoreside pumpout hose is turned to "off" and fits your deck through-hull. If it doesn't, you may need an adapter, usually available at the pumpout.

Holding tank installtion illustration

Typically, you press a switch to start the shoreside pumpout. With the pump running and ready to pull a vacuum, place the rubber-ended nozzle into the deck fitting and slowly open the valve. If the hose has a sight glass, you can see the wastewater being pulled from the tank. If not, you can tell by the sucking sound when the process has started and when the tank is empty. Once the pumpout is complete, keep the pump running to be sure that all the wastewater is sucked out of the hose. Then close the valve and consider flushing some freshwater through the head and pumping that out as well.


Periodically pour a little vegetable oil into manual pump heads. The oil lubricates the pump's valves and seals, making pumping easier, and prolongs the life of the pump.

If there's a bucket filled with water or a disinfectant mixture by the pumpout station for disinfecting the pumpout hose, simply open the nozzle valve, put the nozzle into the water or disinfectant, allow it to pull up a small amount of the disinfectant, and turn the nozzle off, being careful not to let the disinfectant run into the water. You're now ready to coil the pumpout hose as you found it and turn off the pump. Some stations don't have an "off" switch; these are on a timer or will automatically turn off when they sense that they're no longer pulling blackwater.

Troubleshooting The Pump

Occasionally, the pumpout machine doesn't run or creates insufficient suction even though the unit is running. The most common issue is a loss of prime or a worn-out diaphragm. If the machine isn't working, it's best to report it to the marina operator and wait for the staff to fix it, or you can go to another marina.

Boat Sewage: The Facts

Sewage regulations are some of the most misunderstood boating laws:

  • Any installed toilet on a boat must be connected to an approved marine sanitation device. In most cases, this is a Type III holding tank. Other options include treatment devices.
  • It is illegal to discharge UNTREATED sewage from a boat on any inland waters and within 3 miles of shore in coastal waters.

Troubleshooting The Boat

If the pump is working properly but nothing is being pulled from your tank, here are some suggestions. Perhaps the pumpout hose in your vessel is clogged. This often happens when you overfill the holding tank (which clogs the hose with toilet paper or waste) or when the boat heels and sloshes wastewater into the pumpout hose. Clear this by running a plumber's snake down from the deck.

Pump out station

Most pump out holding stations have clear instructions posted, on how to use the facility.

The most common culprit is a clogged vent hose or one that's too small for the pump's suction; as a result, not enough air enters the tank to replace the volume of the wastewater being removed. To determine if either of these is the problem, watch the tank (if possible) to see if the sides pull in while pumping. If they do, the tank is under a vacuum. Be careful, as the holding tank could crack or implode!

The usual cause is a vent line clogged from waste material or at the through-hull where the vent line exits. Many through-hull vents come with stainless-steel screens to keep out spiders and wasps. These may corrode, leaving residue that prevents the tank from breathing. Often, other debris clogs the hole. Check the vent hole in the hull first.

If the vent hose is clogged, the easiest way to unclog it is to use an electrical snake (the one I keep is plastic and round). Run it down the hose until you've hit the clog. You can gain access inside the boat, preferably where the vent hose connects either to the through-hull fitting or to the top of the tank.

Another issue I've seen is when the tank fills even though you're pumping it out. This is almost always due to an open through-hull at the end of the macerator hose, an arrangement that's illegal in many areas. That through-hull should be locked shut in those areas, unless the Y-valve is locked, so that waste can't go overboard. Most holding tanks sit below the waterline, so when the through-hull and/or Y-valve (if you have one) is open, water can flow backward into the tank while you're pumping it out — and at other times, as well.

Common Head Questions

Q: Why does my boat always have a lingering odor that smells like the head?

A: Discharge, macerator, and pumpout hoses all have a finite lifespan. Once these deteriorate, gases can leak through them. Deteriorated hoses often are gummy to the touch, indicating excessive age. Replace the hoses with a high-quality waste hose. Also, if you use an aerobic "sweetening" product but don't get enough oxygen into your holding tank, or if you also dump in anaerobic products such as household cleaners, the aerobic product won't work well, if at all.

Q: How can I fix the horrid smell outside of the boat when someone flushes?

A: Consider adding a charcoal filter into the vent line. Make these yourself with parts available at most hardware stores, then fill them with activated charcoal, which you can find at a pet store. Or purchase one of the commercially available products.

Q: Why does my incoming water stink when I flush the head?

A: The common culprit is anaerobic bacterial growth after saltwater has sat in the feed line. Anaerobic bacteria produce an unpleasant sulfur smell, similar to the smell that comes from a holding tank that isn't aerating well. These aromas are often confused with those of human waste, but they aren't connected. Pumping water through the head much more frequently helps, as does pumping vinegar through and leaving that in the hoses instead of saltwater when you won't be using the head for more than a week. You can also use an inline deodorizer, such as the K02-Knocks-Out-Odor kit by Raritan. The one complete solution is to switch from saltwater to freshwater for flushing by running the intake line for the head from the freshwater tank. Adding an electric vacuum head minimizes the water use.

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Brian Mistrot

Contributor, BoatUS Magazine

Brian and Christine Mistrot have been cruising Florida, Puget Sound, and the Gulf Coast since their children were born.