What is the strange white worm like thing at the base of my fishes tail?

Fish poop. They poop in one long strand. Normally it doesn't stay connected for more than a couple hours. But 3 days though? Probably the best thing to do is wait another day. And if its still connected then call a pet store and ask them what you should do. They have fish and I'm sure this isn't the first time something like this has happened . It may be something as easy as using a pipe cleaner or something And breaking the strand.