Beep, as to your impending undershreddie conundrum...
... the correct technique for assessing whether or not one's undercrackers are too malodorously pungent for human consumption is none too dissimilar to the tried and testing method for ascertaining whether one's spaghetti is cooked to perfection or not. In other words, sling 'em at the wall and if'n they stick, it's time to change to a less polluted pair.
Or..........
.......... maybe you could just hand wash them.
HTH