I've never done anything to clean a tent other than sweep it out, wipe the walls/floor with a damp rag, and at the end of the season hose te outside off and let it dry very thoroughly. There's no need to involve either a washing machine or detergent. I did attempt to vacuum the dog hair out of a tent I was selling, but last I heard from the buyer, it was still there.

My understanding is that once the polyurethane coating starts to deteriorate (usually noticeable from the nasty smell), the only thing you can do is discard it. Getting the old coating all off and trying to apply a new coating are, I understand, not worth the effort Of course I've had only silnylon tents in the more recent past. There is a spray product with which you can beef up the silicone (which is impregnated into the fabric and is not a coating).