Here are some options you could use, depending on the context:
* A load of laundry: This is the most common and practical way to refer to a collection of items being washed.
* A batch of washing: This implies a specific group of items being washed together, perhaps with a particular purpose.
* A pile of laundry: This emphasizes the quantity of items needing to be washed.
* A basket of clothes: This is a more specific way to describe a group of items ready for washing.
You could also be more creative and use:
* A flurry of fabric: This is poetic and emphasizes the movement of clothes being washed.
* A cascade of colors: This evokes the image of colorful clothes being washed together.
Ultimately, the best collective noun depends on the specific situation and the effect you want to achieve.