Skills | Techniques & Best Practices


Outboard Flushing,
The Right Way

By John Tiger

It sounds simple, but hang on! There's a right and a wrong way to perform this essential task.

The Old-School Way

Photo of Yamaha flush muffs
Photo: Yamaha

Flush muffs are the most common way to flush an outboard; they're available at most marine stores and online resellers. They're inexpensive, and easy to use. Connect to a garden hose, fit the muffs over the engine's water intakes on the sides of the gear case, turn the water on, start the engine, and let it run. That's it, with the following precautions:

  • If your engine has additional water intakes that are not being directly fed water via the flushing muffs, they must be sealed off with a bit of duct tape, or overheating may occur.
  • If your engine doesn't have water intakes on the sides of the gear case, you will need a special type of flushing attachment that covers the front of the gear case. These can be purchased from aftermarket shops.
  • When attaching the muffs, be sure they cover the water inlets completely and don't pop or slide off when the water is turned on.
  • Be vigilant, and don't leave the engine while flushing. Watch the engine's "tell-tale" overboard water indicator to ensure that the engine is pumping water.
  • The engine should be kept in neutral and not run above a fast idle speed (1,000 rpm maximum).

Built-In Flushing Attachments

Photo of outboard flushing Photo: John Tiger


Make sure you have a hose, water source, and the keys to the engine before you start flushing.

Built-in garden hose attachments are a standard part of many outboards manufactured in the past decade or so. These attachments make flushing easier, because the engine usually doesn't need to be running (and in some cases, should not be) to accomplish the flushing procedure. Simply check to see if your engine has this attachment (look in the owner's manual), find the connection point, hook up a garden hose, turn on the water, and let it flow for 10 minutes. This is handy if you can't start the engine (dead battery, for example) or if your neighbors would balk at your engine's noise. Some caveats about using a flushing connection:

  • Be careful not to cross-thread the connection. Many are plastic, and can be ruined quickly if threaded incorrectly with the brass fitting of a garden hose.
  • Pay attention to the manufacturer's recommended procedure. See below.

Flushing Bags

Photo of a vinyl flushing bagPhoto: Yamaha


Soft-sided heavy plastic or vinyl flushing bags fit around the lower unit of the engine and fully enclose it.

Flushing bags are soft-sided heavy plastic/vinyl bags with a support framework, designed to be fitted up and around the lower end of an engine and fully enclose it. A garden hose is attached to fill it and keep water circulating; the engine is then started and run much the same as with a flush muff attachment. Flush bags allow for engine-on flushing without the loud noise of the engine's open exhaust. Online, google "outboard flushing bag," and several options pop up. As with other flushing devices, caution must be exercised:

  • The bag must fit pretty snugly around the engine's midsection, and be tall enough to reach well above the water intakes.
  • The propeller should be removed before installing the bag.
  • As with a flush-muff attachment, engine speed should be kept to a fast idle, no more than 1,000 rpm. The engine should be kept in neutral.


 Recommended Articles
Gray rule

Thumbnail photo of a shut-off lanyard4 Steps To Take If Your Outboard Quits

You're putt-putting along pretty as you please, when suddenly your outboard dies. Major bummer!

Thumbnail photo of testing Torqueedo Travel 1003The Latest On Alternative Outboards

Foundation Findings #52: Our team takes a close look at how environmentally friendly outboard motors perform

Thumbnail photo of checking engine temperatureBoat Engine Troubleshooting

What's that funny smell? Do you hear a strange noise? Stop and trust your senses

BoatUS Magazine Is A Benefit Of BoatUS Membership

Membership Also Provides:

  • Subscription to the print version of BoatUS Magazine
  • 4% back on purchases from West Marine stores or online at
  • Discounts on fuel, transient slips, repairs and more at over 1,000 businesses
  • Deals on cruises, charters, car rentals, hotel stays and much more ...
  • All For Only $24 A Year!

Join Today!