I can't believe some people drain their washing machines into drywells, wait, that was me. Shoulda, woulda, coulda,, sometimes we get into some problem areas, its easy if it isn't you in that spot. Of course its not the correct thing to do maybe but it happens. Any way, on to your question, I'm a little surpriesed your sump pump keeps up with your washing machine, that is alot of water at one time, must have a good size pit to do that. I'd watch while the machine is emptying to see that the pump is keeping up. Maybe a small load, wouldn't seem so if its a large load, of course if you have a front loader, all bets are off.