During your Everest Base Camp Treks, you can also enjoy the basic amenities such as a hot shower and laundry. The teahouses/lodges in the lower regions have westner-style bathroom facilities with modern design.
You will be able to take a hot shower and enjoy laundry services to maintain your hygiene throughout the trek. However, as you ascend to higher altitudes, the modern amenities become pretty sacred. For the bath, you can buy a bucket of hot water, and the laundry service is of standard level.