Washer drain keeps backing up?

J., No. You can't just let washing machine water just run out into the street. It's really funky that somebody installed those machines outside but, uming that the drain is adequate & properly installed, the reason it keeps backing up is probably just because it needs to be cleaned (snaked) That's why it's backing up. You can certainly put those machines in your garage as long as you have the room for them but, you'll need a drain, a dryer vent, & power to run those machines. Good luck