Took a bit to find this, but I remembered a lecture by a Wyeast lab tech:
The "tried and true" method of washing yeast utilizes phosphoric acid (H3PO4) to acidify the yeast slurry to around pH 2, where it is held for a given amount of time, ranging from two hours to overnight. In theory, undesirable organisms are destroyed by the low pH and trub is removed from the yeast. The healthy yeast remains suspended and is used for pitching, while dead cells and trub collect at the bottom of the washing vessel.
I don't think a little lactic acid will slow them down.
Remember one unassailable statistic, as explained by the late, great George Carlin: "Just think of how stupid the average person is, and then realize half of them are even stupider!"
"I would like to die on Mars, just not on impact." Elon Musk