Who would use a plunger on Shabbos when it WASN’T important to do so? Please, people! A bissel seichel.
I’m not sure what you mean.
There is a machlokes whether plunging a toilet which is only mildly stuffed is muttar or assur on Shabbos. Most rabbonim would probably tell you that if there is another toilet available, don’t plunge it, but if there is only one available, one can rely on the lenient opinion.