I need to attach a hose to this spin down filter to be able to easily flush. What attachment do I need? Regular garden hose too wide to fit in threads

Our plumber installed it and did not leave any packaging. When you say "you might add an adapter" does that mean it might or might not work?

The filter is designed to use the 1/2" ball valve included with the package. The threads are 1/2-NPT. You might add an adapter to make a garden hose connection.