Boat Thru-Hull Fittings: How to Match a Marine Drain Connector to Your Deck and Bilge Setup

When you're working on marine pumps, plumbing, and sanitation, the thru-hull fitting is the part that carries water from a deck drain or bilge pump through the hull. Pick the wrong size or angle and you're left with a connector that doesn't align with your hose run or a drain that won't sit flat. The four fittings listed here show the main trade-offs: a 3/4-inch stainless steel thru-hull, a 1/2-inch stainless steel thru-hull, a black 90-degree connector, and an adjustable plastic hose connector.

Quick Take

For a permanent drain line where corrosion resistance matters, the 316 stainless steel Alastin model is a solid choice. For a compact hose run using the same stainless steel material, the smaller Alastin fitting costs less. If you need a right-angle deck drain or bilge vent port, the 90-degree black connector gives you that elbow in one piece. For a hand-installed hose connection that can adjust to a 1-1/4-inch opening, the premium hose connector is the adjustable option and the lowest listed price.

Listed Price Comparison

Decision Matrix

3/4" Boat Thru-Hull Plumbing Fitting 316 Stainless Steel Marine Drain Connector

This Alastin connector gives you 316 stainless steel in a larger diameter, and it's suited to sailing yachts, fiberglass yachts, inflatable yachts, and commercial yachts. Installation is designed to need no extra tools. That makes it a good match for a permanent hull drain on a boat that's often in the water. The limitation is the largest listed price of the four, and the diameter won't suit a smaller hose run without an adapter.

1/2" Boat Thru-Hull Plumbing Fitting 316 Stainless Steel Marine Drain Connector

If your hose run is a compact line, this Alastin stainless steel thru-hull gives you the same high-strength material and tool-free installation approach as the larger version but in a more compact diameter. It's designed for sailing yachts, fiberglass yachts, inflatable yachts, and commercial yachts. The listed price is below the larger stainless steel model, so it's the lower-cost metal connector in this set. The limitation is the smaller opening: it's made for a narrower hose, so it won't directly fill a wider hull opening.

thru Hull Fitting Boat Plumbing Fittings Easy to Install Premium Hose Connector

This connector uses a thickened PP plastic body that is wear-resistant, and it fits openings sized for a 1-1/4-inch hole. The length adjusts from 2 inches to 4 1/2 inches, so you can adapt it to different hull thicknesses, and it installs by hand with threaded nuts rather than tools. It is the lowest listed price in the group, making it a low-cost way to add a thru-hull hose connection. The trade-off is the plastic material instead of stainless steel, so it's best matched to a hose hookup rather than a permanent metal drain. The color is listed as black.

Boat Plumbing 3/4 Inch 90 Degree Thru Hull Fitting Connector Black

This black fitting turns the drain 90 degrees, which is useful when a deck floor drain or bilge pump vent port needs to make a sharp bend. The PVC construction is compatible with 3/4-inch fittings, and it can be used on boats, yachts, trucks, and tractors, which makes it a versatile part. The listed price sits between the stainless steel models and the plastic hose connector. The limitation is the fixed right-angle shape and the size: if your hose line runs straight or uses a different diameter, this elbow won't adapt on its own. It's also a plastic/PVC part, not metal.

Final Recommendation by Use Case

For a permanent drain on a yacht, go with the stainless steel Alastin thru-hull in the larger size. For a narrow metal line, the smaller stainless Alastin connector is the direct match. For a right-angle deck drain or bilge vent, the black 90-degree connector gives you the bend. For a hand-installed hose connection that can adjust to different hull thicknesses, the premium plastic hose connector is the adjustable pick.