How to Clean Your Boat's Bilge (Legally, and Without the Smell)

Open all the hatches and look at the bilge water with a flashlight. Rainbow sheen, dark film or a fuel smell means don't pump it overboard. Note where the oil seems to come from: under the engine, the transmission, the fuel filter, the steering pump or the stern drive.

Lay oil-absorbent pads or pillows on the water to soak up the oil before you do anything else. New York Sea Grant lists this as the first step before pumping a bilge. Use contained pads or socks, not loose powder or granules, which the BoatUS Foundation warns can clog your bilge pump.

Once the oil is soaked up and the water is clean, you can pump it normally. If there's still any sheen, remove it with the wet/dry vacuum or a hand pump into sealed containers for disposal ashore, or use your marina's bilge pumpout. Pick out debris by hand: leaves, zip-tie ends, hair, fishing line and bits of food.

PassageMaker's advice is to scrub by hand first rather than flooding the bilge with soapy water, which just spreads oil residue over more surfaces. Work one small area at a time: spray, brush, wipe, dry. Use rags and change them often. Wear gloves; bilges are full of sharp clamp edges and zip-tie ends.

If grime is stubborn, a bilge cleaner can help, but follow the label exactly and plan where the dirty water will go: into containers or an approved shore facility, never overboard. Rinse with fresh water, and capture that rinse water too.

About "pour in, go for a run, pump out" labels: some bilge cleaners, Star brite's Heavy Duty Bilge Cleaner among them, tell you to pour the product in, run the boat for an hour or more so the motion scrubs the bilge, then drain or pump it out. Star brite's own directions also say to soak up any fuel or oil with an absorbent first. Do that, and plan the "pump out" step for a pumpout station or containers ashore: once the cleaner has emulsified oil, the water can still carry it overboard even if you can't see a sheen.

BoatTEST notes that the key to an odor-free bilge is a dry one. Vacuum out the last of the water, wipe down with rags, and leave hatches open to air it out. Look for any standing water that isn't draining.

Limber holes are the small drain holes through stringers and frames that let water flow to the lowest point where the pump sits. Sailors for the Sea advises keeping them clear. Push a pipe cleaner, stiff wire or a long zip tie through each one to clear debris. If a hole is blocked by something you can't remove, or water is trapped in a section, get it sorted before the next trip.

Lift out or reach the bilge pump. Clean hair, sand and debris off the strainer or intake screen. Lift the float switch by hand (or use the test button) and make sure the pump runs and the switch moves freely. Wipe off any oily film from the float; oil can make it stick. If you switched the pump off or to manual so it wouldn't pump dirty water during the clean, BoatUS reminds owners to put it back on automatic when you're done. Tie a tag on the switch as a reminder. A BoatUS article on bilge care suggests repeating this pump-and-switch check about monthly from the helm switch, since debris in the float, sensor or pump housing is what stops a pump from working at full capacity.

Odors usually come from something feeding the bilge, not the water itself. Check:

• Shower and icebox drains that empty into the bilge instead of a sump (BoatTEST suggests plumbing them into a sump)
• Gray water sumps that are full or have a dead pump
• Head hoses that let odor through (PassageMaker's cloth test: drape a clean cloth over the hose, leave it a while, then sniff it)
• The anchor locker with a wet rode or mud
• Fish boxes or hatch gutters draining into the bilge
• Old fuel or oil dripping from a filter or fitting

PassageMaker suggests hydrogen peroxide in sumps and the bilge to kill bacteria, and warns against straight bleach, which can react with some plastics down there.

Fix the leaks you found: a dripping stuffing box, a loose hose clamp, an oil leak under the engine, a leaky deck fitting or hatch. Look for rust on clamps and engine mounts as a sign of constant moisture. A dry bilge stays clean much longer.

Place an oil-absorbent pad under the engine and an absorbent sock in the bilge, as Sailors for the Sea and the Virginia Clean Marina Program recommend. Secure them so they can't drift into the pump or float switch. In the BoatUS Foundation and Duke Marine Lab test of 21 products, many didn't work well and some were toxic, so choose a contained product with good test results and replace it when it's saturated.

Used pads, oily rags and containers of oily water are hazardous waste in many places. Take them to your marina's oil recycling station or a local household hazardous waste collection site; ask your marina or town what's accepted. The BoatUS Foundation notes that in many areas, absorbents dripping oil must go to hazardous waste, while ones that fully lock in the oil may go in regular trash, depending on local rules.

Ventilation keeps the bilge dry and fresh. After a wash or a rainy day, open the engine hatch and lockers for a while so air can flow through. Log the bilge clean in BoatMend and check the bilge, pads and pump at every outing.