What Size Is the Drain Plug on A Boat?

What Size Is the Drain Plug on A Boat?

Note: As an amazon associate I may earn a small commission from qualifying purchases if you click to amazon from my site and choose to make a purchase.You can read my complete affiliate disclosure for more details

What Size Is the Drain Plug on A Boat?

A drain plug is a device used to prevent the build-up of liquid pressure in a plumbing system by redirecting the flow.

They offer protection from sewer gases released from the drainage system, which can cause a potentially explosive mixture and potential water damage.

The average boat drain plug has a 3/4-inch hole with a 1-inch hole on end. The three-quarter-inch hole drains any water that may have accumulated in your bilge area. You can typically find this near the bottom of your hull at the front, back, or even on both ends.

When using this drain, you should always cover it with a bucket to prevent water from splashing around when emptying your bilge area. The 1-inch hole is specifically for draining your tanks.

The hole for your water tanks will always be bigger than the hole for your bilge. The hole on the end of the drain plug will be a different shape than the other drain plugs.

This also applies to shut-off valves; they will have a special wrench that only fits that particular valve and no others.

Drain plugs are generally used on boats over 12 feet and have a watertight hatch to contain the water from the bilge.

What Size Is the Drain Plug on A Boat?

Cruising boats typically don’t have a drain plug; they use a manual sink cock that opens up when you open the drain cock. This is typical for most cruisers and sailboats under 12 feet in length.

Are There Different Size Drain Plugs in A Boat?

Emergency Spare PlugYou can find this on newer boats. The plug seals a drain if something gets lodged, preventing water from rushing out.

This type of plug is typically larger than the traditional one above and has a longer stem that tapers down to fit through an opening in the drain.
T-Handle Drain PlugsWe use T-Handle plugs on larger water drain fittings. The plug handle (the part you turn) is longer than with a traditional plug and has a 45-degree diagonal cut out of it.

This allows you to turn the handle using a flat-head screwdriver as leverage instead of using two hands.
Strainer PlugUsed by many powerboats and sailboats when docked, having a strainer prevents crud from entering the boat through the drains.

The strainer plug is smaller than the emergency spare and has an even smaller opening inside.
Manhole PlugThis type of plug also has a 45-degree cut-out in the handle, but it is a square plug.

You can find the lock nut for this type of drain on either end of the plug instead of on a T-Handle Plug, where all three are at one end.

This design allows more room for sediment to collect between the nut and the handle. Also, it’s easier to turn the handle of this plug.
Sealed Drain PlugThis is the oldest style of drain plug. All three components lock together with a single lock nut, creating a seal that keeps water out of the boat.

These plugs are very difficult to remove once you install them.

Should A Drain Plug Be on The Inside Or Outside Of A Boat?


A drain plug is an O-shaped fitting that allows water to flow from one area to another without allowing it to get back in. It’s inserted on the outside for vessels over 15 feet long and inside for smaller boats and canoes.

The larger difference between the two plugs allows you to pull them more easily, making it easier for moored boats or stationary to empty the water of their holding tanks.

However, the drain plugs on larger boats comprise galvanized steel to prevent corrosion and rusting.

The inside/ outside difference also depends on what kind of boat you have.

If it’s a hydrofoil boat and you remember to put the plugin only after the foil completely retracts and the boat is back on land, it’s an outside plug.

The hydrofoil fills with water, which helps stabilize it in the water. It would be unstable if it didn’t have water as it has less weight. For clarification on your boat, refer to the owner’s manual.

Another reason for draining the water from your boat is if you accidentally leave some water in it and go on a long drive.

The water will expand and cause the boat to buckle due to extra weight. You need to drain your boat after a long drive or use a drain plug in the holding tank so that no water remains in the boat.

What Size Socket Is A Drain Plug?

Over-tightening drain plugs can cause damage, such as stripping the threads on the bolt and breaking the seal on the plug, which can cause a leak or a flood.

Check if the drain plug has an external thread, which means you can remove and re-tighten it. In this case, use a wrench to unscrew the plug one-quarter turn each time you perform an inspection.

Also, ensure that no water runs out of the sink after tightening it. If water still comes out or it’s making a bubbling noise, loosen the plugin small increments until all those issues are gone and re-tighten by hand.

If there’s no external thread, tighten it by hand about two to three turns after each inspection. If it still leaks, put the plumber’s tape around the plug and re-tighten.

What Size Is the Drain Plug on A Boat?

You should replace the drain plug if the problem persists.

If you want to remove the water from a sink with no external threads, use a wrench or another tool to tighten the plug until the water stops dripping and completely dry out all holes for drainage.

Do You Need to Torque the Oil Drain Plug?

Yes! The oil drain plug on your boat comprises a high-quality sealant that requires torque to secure. If it has a poor design, the sealant can crack or break under high torque, and the tower can leak or even fall off.

Always use a torque wrench and ensure enough clearance to allow for proper rotation, especially in larger models.

More importantly, when you are replacing the plug, it’s important that you also change the gasket at the same time.

The gasket will help keep any residue from entering your engine and causing damage that could be expensive to fix later on. You must check the manual for your boat model if you need help with how to do this.

Not all oil drain plugs require high torque, but those made of steel instead of brass will. These are usually in older models; you can identify them by design and gasket.

In these models, you will need to use a torque wrench to ensure you are using a sufficient amount of torque. By using a wrench, you also help prevent stripping the threads and damaging the plug.

For newer models of boats, you must ensure the new gasket is compatible with the old one. But; they will not fit without damage.

Even though your manual might say they are interchangeable, it has given proof that doing so will permanently void your warranty.

Should You Replace the Drain Plug with Every Oil Change?

Yes! A drain plug is a rod-shaped device that fits into the bottom of a boat’s hull and prevents water from entering when the vessel is on land. As with all things mechanical, you must replace it whenever it gets worn out or corroded.

There are three main reasons your drain plugs need replacing every time you change your boat’s oil. First, the normal in-and-out action of the oil filter will not clean the threads of the drain plug.

Second, although an old oil filter can still trap larger particles efficiently, its ability to prevent smaller particles from filtering through greatly diminishes with regular use and age.

Third, the oiling system pressure in your boat can cause the drain plug to corrode.

The most suitable way to remove the drain plug is to use a large flat screwdriver or a similar tool to pry it up from the bottom of the hull.

Another alternative is a long punch-type tool with a pointy end.

If you use one of these approaches and the drain plug still does not want to come out, you could file down its surface using a metal file or sandpaper and then use an oil wrench.

5 Drain Plug Standard Types

Plug TypeMaterialWeightDimensionsManufacturer
Dorman 090-167 Oil Drain Plug Standard M18-1.50,

Head Size 17Mm Compatible with Select Volvo Models, 5 Pack
Corrosion resistant material‎5.4 Ounces‎6.25 x 2.75 x 2.75 inches‎Dorman Products
Dorman 921-131 Oil Drain Plug Standard M14-1.50,

Head Size 17mm for Select Audi/Volkswagen Models (Pack of 5)
Corrosion resistant material3.67 Ounces8.4 x 6.4 x 4 cm; 104.33 Grams‎Dorman
Dorman 090-024CD Oil Drain Plug Standard 5/8-18,

Head Size 9/16 In. Compatible with Select Models
Corrosion resistant material1.44 Ounces‎1 x 1.61 x 4.02 inches‎Dorman Products
M14x1.5 Magnetic Oil Drain Plug for Engine and TransmissionStainless steel‎1.44 ounces5.87 x 3.43 x 0.79 inches‎K-Motor Performance
Dorman 090-033CD Oil Drain Plug Standard M14-1.50,

Head Size 17mm Compatible with Select Models
Corrosion-resistant materials‎1.44 ounces‎1.05 x 1.55 x 4.09 inches‎Dorman Products

Why Does the Drain’s Material Matter?

The boat drain material matters because it determines how long your boat will last and what materials are safe on the bottom of it. The material also affects how well your boat performs.

A fiberglass drain will quickly break down, while a stainless-steel drain lasts longer and keeps carpets, floors, and fabrics cleaner. When choosing a drainage system, pick one best suited to your lifestyle and budget.

There are three main types of boat drains ,fiberglass, stainless steel, and a hybrid of fiberglass and stainless steel. They are made differently and last for different amounts of time.

Fiberglass drains are lower in cost than stainless-steel drains, but they erode quickly. Stainless steel drains last longer but cost significantly more than fiberglass options.

Hybrid fiberglass/stainless-steel drains are the most expensive and last the longest.

Fiberglass drain systems come in three main types: solid, plug, and float. These three types are for different things.

Solid-type drain systems are used for deep boat storage or to convert your boat from open to closed storage.

The plug-type is designed to be installed in a tube most commonly found on boats, while the float-type is generally easier to install than other varieties.

The plug-type drain system is more commonly found on newer boats. These systems come with a mini-valve that allows the boat’s drain to work out of its floor.

Older boats with fiberglass floors are much harder to install, while newer boats have a much easier process for installing these drains.

Usually, a drain system will include a water trap and an overflow tube. The water trap will stop any water entering the boat in a “U” shape, leading it to the overflow tube.

This type of system is known as the plug-type drain system.

The float-type drain system keeps the boat cleaner for longer. You can install these drains in various ways; however, most people like to install them between the floorboards on either side of their boats.

These drains can be installed from the side or from underneath. When installing these drains from the side, you will need to be experienced.

5 Types of Boat Drain Plugs

Boat Drain PlugsFeatures
1″ Transom Drain with Plug-Watertight seal · Retaining legs · Replacement plug RF738 · Chromed brass body · Black nylon plug UV stabilized · Equipped with a retainer to help prevent loss
WEST MARINE Flip Lock Drain Plugs· Drain plug with multiple applications · Brass/rubber construction · Three sizes
MOELLER 1/2″ Brass Transom Drain Plug Dock· Installs in seconds with no screws required · Great reminder for operators to attach safety “Kill Switch” per U.S. Coast Guard regulations · Lanyard Not Included
PERKO Garboard Drain Plugs· Stainless pin for easier plug removal by hand · Cast bronze for corrosion · Brass Plug · Bronze Flange · Plugs fit standard 1″ drains
T-Handle Drain Plugs· User-friendly Choice of Brass or Stainless steel. · Offered to fit 1″ and 1 1/4″ diameter holes.


Boat drain plugs are very important in maintaining the boat and are also one of the reasons a boat is not worth as much. A good transom drain plug should be easy to install, comfortable to use, and affordable.


Hi! I' am Tom. I was a manager in one of the biggest stores for over 10 Years, am also an SEO by night. I don't like to call myself a blogger; they are very analytical, do email marketing, and know all SEO stuff. I faced many questions from customers about different products, and there was hardly any help on the internet. After learning all the things about these products as a manager the hard way, I decided to start a blog and help other people.

Recent Posts