I think it's disgusting to not wash trainers in the washing machine. Trainers smell because of the bacteria left in them from all the sweat coming from your feet. Fabreeze or whatever it's called, might mask the smell for 5 minutes but it's not going to kill off the bacteria. Only a hot wash will do that.
I actually find it very satisfying getting trainers washed in the washing machine. All the white bits are nice and gleaming again and once they've been stuffed with newspaper and sat below the radiator (not ontop, because too much direct heat can melt some glues used in soles etc) they feel all tight, tacky (talking about 5tens here) and new again.
As has been said. If they're mega dirty, give them a brush off to get all the stones and dog shit off them first. Remove the insoles too. I've also found over the years that leaving in the laces works best. If the laces are white, it's murder trying to get them back to where they were previously as they'll never be 100% clean and will be full of tide marks.