There is safer ways I'm sure, but the best way I know is wash it with good ol gasoline first to get the oil off, then squirt liquid soap all over it and keep rinsing it with water from a garden hose or a shop sink (warm water is best) if you have one. It takes a while to get all the soap out when you squirt it directly on the filter , but that insures you cleaned it thoroughly, IMO.
I recently purchased a No Toil filter which uses biodegradeable filter cleaner, filter oil, and grease. You can use their bio stuff on your current filter but you must clean it first and get all of the petro based chemicals out of it. Then buy the No Toil filter kit which sells for 16.95 and comes with filter oil, cleaner, and grease. Works great and no more harsh chemicals to dispose of. You can safely dump No Toil in your kitchen sink. I will never go back to the bad stuff. Hope this helps.
I use mineral spirit and dishwashing soap. Soak the filter in mineral spirit first to get most of the oil off and then wash the filter with the dishwashing soap and warm water. It works great and there is nothing that can go BOOM! it is not flammable. You can reuse the mineral spirit, just let it sit for a day or two and everything will go to the bottom. Make sure that you use Dishwashing Soap...it cuts grease/oil really good.
I cannot even think of going back to the solvent after using No-Toil.
After 19 years of crapping around with chemicals I tried No-Toil and I love it.
At croom I swamped my bike to the point where you could only see the grip sticking out of the water and I sucked in water but the filter was still tacky and useable. All I had to do was flip the bike upside down with the plug out, put in in gear, spin the rear tire, flip it back over, put fuel/premix in the cyl., and start.
I made it back to camp and Pulled my seat off to remove the filter and was very suprised to see it was still tacky and DRY!!!!