I rarely wash my snowboard clothing. Think about it, it repels the water and dirt on the mountain anyway. You worried about sweat? Well, your base layers should take care of that.
I do have one jacket I wash every year, but I wear it off the mountain a lot too. With this jacket, I just toss it in the washer with a little bit of detergent on delicate wash with cold water. Then I hang dry it. If the jacket doesn't bead off water anymore, I use a Nikwax spray on water proofing spray after the jacket dries. Careful though, that stuff stinks. Make sure you do the spray on outside or somewhere with good ventilation. Wear a mask if you can.
So yea, no real need to wash jackets that you only use for snowboarding unless you don't layer correctly and sweat like a dog it.