Hate to be the bearer of bad news but... if it's a garter snake it may be up inside your washer or in the dryer from underneath.
If you want to know for sure it's still in the laundry room, sprinkle either flour or baby powder around the washer / dryer and in the doorway.
Leave it alone and you'll be able to see if there are "trails" in the dust.
The only way to be sure it can't get out of the laundry room is to tape a very high piece of cardboard or such across the entry way. They can get through teeny spaces so you have to have it full sealed off to keep it from going into other areas.
If you have a cat or dog, they can corner it (if so inclined). They might strike and could tag you so don't anger it.
They are generally very docile and can be picked up and put outside without any harm to either of you. It probably isn't thrilled to be stuck inside either.
Good luck (some cultures would consider this very lucky)