Hey Mary, it's good to see you back on here.
I mean, it won't wash EVERYTHING away - you can still use it - but the potash will be gone. There's still good stuff in it; it just won't be as beneficial. However, if you need more soil for the garden, it's all in the ground underneath your firepit. Dig that dirt up and use it. It will have activated biochar in it as well, if it's been in the ground a few seasons. It should be easy to dig, and blackish.