Hi Lynn,
I hear now and then that on rare occasion, left-over pieces of drilled hole material for the fresh and waste water tanks, can end up inside the system. You might have found one such piece. It is very hard to say if it damage your macerator, but I favor the idea that your macerator is fine. I wouldn't know about the electric tank valve.
It is a great idea when first purchasing any new motorhome, to fill both waste systems to their tippy tops with fresh water and open one waste system at a time. You want the water to rush out as fast as possible until empty, done through the manual dump opening. This to try to expel any such plastic debris. How many times is up to you.