Thanks to a standard that extends back more than 30 years, most marine bilge related products use 1-1/8" hose connections rather than the more common 1" inside diameter size. To make matters worse, many fittings are advertised universally as being designed for 1" hose, even though the actual nominal size of the fitting is 1-1/8". As you can imagine, it can be difficult to make a fitting that's too big fit into a hose that's too small. Unfortunately many ballast systems actually do use a true 1" fitting somewhere in the system, which means that 1" hose must be used throughout.
We have a lot of customers contacting us why it's so difficult to get the 1" fittings they purchased inside the 1" hose they bought from us. Refer back to the paragraph above for the answer, but basically the fitting is 1/8" too big for hose. Fortunately with a little knowledge, it's actually quite easy to get the fitting to slide into the hose. It's a question that's asked enough that we decided to put together a little video that shows the process: