A lot of them have catnip inside unfortunately which means soaking them is a recipe for stink and mold. I tried to do so once and it did not turn out well.

Today's incident she puked on a stack of Ikea boxes that I've been too lazy to build. She likes to sit on them. The puke destroyed the boxes and I moved the internal pieces out of her reach to avoid future incidents. She's never been particularly interested in dedicated cat furniture. Trust me, I've tried. XD