We do not recommend machine washing.

Should it be dry cleaned?

Spot clean with water and mild detergent. Professional clean for a deeper clean.

Again I ask, what is professional cleaning for a cotton bathroom rug?

Cleaning instructions from the manufacturer:

With a dry cotton towel or white paper towel, blot out stain as much as possible. Scrape off any debris. Mix a very small amount of dish soap with a cup of cold water. With a clean sponge and soap mix, gently remove the remainder of the stain. Avoid using excessive water. Blot area with a dry towel. Vacuum regularly. Avoid vacuums with invasive beater bars. We recommend using a professional rug cleaner on an annual basis.