I was getting fairly flat prints at 8x10", but now I'm printing bigger, they are wildly uneven. I'm squeegeeing them pretty thoroughly, and air-drying them face down on screens, and leaving them 24 hours at the darkroom where I go to print. By the time I collect them, they are rippled and decidedly un-flat. Shoving them under books for a couple of days still isn't doing the trick.

What does the trick with flattening? Is it heat, or pressure, or the combination of the two? I don't have access to a dry-mounting press, so is there any reason not to use a normal household iron on the back of them? (With, I would assume, the steam off.)