I pulled my air breather over the weekend, it was pretty dirty. I followed my books recommendation and soaked in soapy water.
after about an hour soak I rinsed it and held it up to the light, it was still dirty. so I repeeted the process, soaking and swishing.
It didn't come completly clean. Is there a product on the market that is safe to use? My filter is the round HD high flow.
I've seen that K&N has a product for cleaning there filters but I'm not sure if it's safe for mine.

Depending on the medium the breather uses you might want to stay away from solvents - they can dissolve more than grease - like the medium you are trying to clean.
Water based: I use Simple Green - removes oil and grease.
I also found a product at the Home Depot - also green - Zep
I've tried Oven Cleaner on everything these days - but be careful that stuff is powerful.

The simple green seems to be safe on most stuff. It cleans the grease off my bicycle chain.

Thanks I'll give the simple green a try.

Just a thought your air filter might be made by K&N. I use their filter on my bike and in the kit they include a cleaner and the oil to make it filter again. You may want to look into that. But if the info that came with the filter says just clean it, I would do just that.

Use it straight out of the bottle - not diluted - works wonders.