It probably is, though you may not be able to get them as clean as with a washing machine. Thinking about my liners they’re probably quite thick and heavy in water. Why can you not use a washing machine. Could you put it in a pillow and tie it before putting in the washing machine?
My washing machine packed up and I had to handwash my fleeces for a week (not guineadad though) but you’ll handwash them like any other item of clothing. The issue i found is that they is that never came as clean as they do in the machine due to the bulk and just not being able to wring them through enough. They also took a lot longer to dry and dripped into the bath with regular wringing for a couple of days as I couldn’t use my machine to spin the water out. I would absolutely hate to have to go back to handwashing them!