There is no question- at least among those who have some knowledge of Tanny's past PUBLIC performances that he managed a 300 pound one hand clean. These were not private sessions with no witnesses, but were in situations among other lifters using the weights they used.
It had long been a goal of his and he worked his way heavier and heavier, with public performances on more than one occasion managing 280 lbs in the one arm clean. Then in 1951 he accomplished 300.
The comparison to Anderson is unfair- TO ANDERSON, who did not at all have the grip needed to ONE HAND clean an Olympic barbell loaded to 300- all of Anderson's heavy dumbell lifts were brought to the shoulder with two hands and then put overhead with one- well not actually overhead- more to the side, with an un-locked elbow, and if you have seen the dumbell Anderson lifted and you believe it weighed much more than 200, then we disagree on that also.