For trips over a week? Find a way to do it there.
We did as much as we could. But when flight back is Isru Chag, there's no way you won't bring back laundry.
"Find a way to do it there" is sometimes easier said than done. While laundromats exist in Moscow, they don't have wash, dry and fold service (I did find online a place that offers such a service, but it wasn't anywhere near where we were). Many don't even have detergent available.