Don't waste your time with soap and water, at least not at first, because you'll be there for 6 months trying to get it off.
There are other brands of filter oil that are advertized as being soap-and-water cleanable, but, they're made out of some kind of veggie or plant oils that, basically, are easier to remove from the foam because they don't stay put as well and aren't as sticky.
There's no free lunch.
FFT needs something that will cut through the oil, so you need some kind of petrolium solvent or equivalent.
After the initial cleaning with solvent, then you can do a second cleaning with soap and water.
Make sure you dry all of the water out of the foam after rinsing it out.
Back in the day, everybody I knew used gasoline.
It cut through the oil well and was so readily available (the bikes ran on it).
However, in these liability-conscious times, the popular trend has gotten away from recommending gasoline.
Some guys also say they've had filters fall apart at the seams from gasoline, but that wasn't a problem for me.
The safest way is one of the ready-made foam filter cleaners made by Maxima, Spectro, etc.
These cleaners cut through the oil and then rinse off with water.
Just make sure you completely dry all of the water out, then reoil the filter and squeeze out the excess oil.