You cannot clean a tent in a washing machine! You will have no control whatsoever over the cleaning process.
Virtually all tents are impregnated and/or coated. There is a high risk of damage to the coating from tearing and folding. Closures and other hard components can bang against the canvas and cause damage to the cloth fairly quickly.
Many tents also have windows. This window film can become damaged easily.
It is best to clean the tent with a strong, soft brush, a special tent canvas cleaner like Sprayhood & Tent Shampoo and lukewarm water. If required, you can first soak the tent overnight in a tub, barrel, or clean wheelie bin, for example.