Can you wash polyester dry clean only pants?

yes you can. all you have to do:

1) Know your fabric and your garment. Some things just shouldn't be washed, even by hand. For instance, your lined wool skirt will likely come out of any wet wash process with a problem: the lining is going to be a different size than the skirt. For reasons known only to the fabric industry, some synthetic fabrics grow when they get wet. And some woolens will shrink to a ghost of their former size if they get soaked. Be careful. On the other hand, many a silk blouse does just fine when hand-washed

2) Fill a sink or wash tub with cool water. Add a small amount of dish-washing liquid to the water (Dove™ and Ivory™ seem to work quite well, and some people recommend Dawn™). Select 1 garment to wash at a time; many dry-clean-only fabrics have not been prepared for a bath and they will almost certainly fade.

3) Allow the garment to soak. Especially with woolen goods, it is better to avoid swishing and rubbing. When your garment is sufficiently clean, remove it from the wash water, fill the sink with clean cool water and rinse. Repeat the rinse until you are confident that the garment is free of grungy wash water.

4) Always air-dry the garment. Roll it in a towel to remove excess water. You can hang woven goods (things that don't stretch), but knit items like sweaters must be dried flat. If you are going to make a practice of washing your dry-clean clothing, purchase a good drying rack.