For various reasons, we ometimes want to run the boat's engine out of the water, or "on the hard." Products are available to help, but I like the one described here. Here is my system in use:

Regulations on some lakes require running the engine to flush "invasive species" out of the cooling system. Of course there are other good reasons, including engine tune-ups, cooling system evaluation, clearing salt water from the system, preventing pump impellers from running while dry, etc.

Here's how I do it on my little ski boat:

MacSkier has two cooling water inlets. Many boats have only one. Here are views of the boat's interior, just aft of the engine. Views are looking down, stern to left, bow to right. Some photoshopping to clarify the image for this use. (Click each for larger images)

   

The device below is used as described below when running engine "on the hard:"

1. A garden hose (with a good supply of water) is connected from the water supply to the "A" fitting.
2. Fitting is connected to cooling hose using the barbed fitting "B". The cooling hose must first be disconnected from the boat's water inlet fitting before making this connection. Note the long cable clamp at inlet #2.
3. A second garden hose is connected to fitting "C," then run outside the boat onto the ground.
4. Before starting the engine, turn on the water supply and run the water until it flows from the overflow hose connected to "C" fitting.