Verging off topic - finishing question

When trying to remove wrinkles from several pieces recently, colors have bled. My advice would be (a) snip a small piece and see how it behaves and (b) if you're thinking of using it on something "important" or "special" or that might get heavy use, don't until you do "a.".

If it's dusty - I would - especially 'cause it'll probably be impossible to really clean after.

Ellice

I'd be inclined not to if you have the choice. The colours may bleed and the sizing (which keeps the stuff managable to sew) will be lost. Depending on what you're intending to make, I'd construct the item and wash it with the piping safely stitched in.

Having said all that, if the piping's really dirty, I s'pose you have no alternative but to wash it and see how it comes out. If all fails, it's not that expensive to buy more.