Prior to knowing the rule of having to wash clothing and skin twice if they have contact with urine, I washed an underwear that was najis from urine in the washer. Did this make any other clothes that were in the washer with it najis? The washer rinses once with detergent water, and then again with absolute water.
The clothes must be washed again because the underwear which was impure with urine requires two separate washes with plain water.