I don't like to take the foam out, because over time, they will lose their shape and won't fit properly. Also, they can go it slightly different and change the fit as well. I have heard people use like a 10-20% alcohol/water solution and just spritz it in the helmet. I guess Febreeze would work as well.
There's a company that makes helmet liner spray. Just spray it in the helmet when it's dry and let it dry. I used to use it on my full face mountain bike helmets. Worked pretty well. This was it.
Does washing your helmet make you go faster? Just kidding i just take my visor off from time to time to get al the bugs off adnwipe the helmet down with lucasol and im ready to go... as for the inside.... just give it a good shaking it'll straighten out!
I have pulled the liner to make sure the snaps are in place and to know my equipment. The foam/liner is a synthetic substance and I feel you could soak and rinse these with no problem. To dry just blot them well with a towel and air dry, or low temp hair dryer, clothes dryer......etc. No rocket science here......my $0.02.
I sneak a box or two home from the laboratory every now and again... Kimwipes are what I use as well, even use them on my glasses without the worry of scratching them.
I just use Windex and a paper towel. Spray the Windex on the towel first so that it is just kinda dmap and then wipe down the entire outside of the helmet, visor and all. Leaves no streaks or bugs. It also helps that I clean my helmet after every ride so that bugs and the like don't really get a chance to dry on it too badly. Then I store it with the visor open so that it can air out...helps it go longer before getting funky.