Help Needed Toilet?

Did a kid flush a plastic toy that is out of reach but clogging things? Mine once flushed a plastic W magnet that was just wide enough to not go down the floor pipe.

What you need to do is turn the water off to the tank. Scoop out the water in the tank, and the bowl. Unbolt the toilet from the floor and carefully tip it. You'll be able to unclog it from the bottom, unless the clog is in the mainline. You may need a new wax ring to reseal it to the floor.

It is a disgusting job and you may just want to spend $50 on a plumber.

Nope.
Something that caustic would dissolve your pipes.
If there's something plastic clogging up your pipes you need a plumbers snake that will either push it past the point where it's stuck or will snag it so you can pull it out.
It can be a nasty stinky dirty job.
I'd happily pay a plumber to do it.

Chances are your pipes are plastic after they leave your house, PVP pipe; so a chemical like you're taking about is highly unlikely made. You could find something and pour it down there but it could do serious damage to your plumbing to the point where you could find yourself replacing all the way to the city main.

Please give us more information. What kind of plastic? Is it stuck on the sides of the toilet? Is it blocking the outlet or the inlet? How did it get to be there?

If it's a piece of plastic stuck in the outlet, lift up the toilet and take it out. Then you have to use a new wax ring to fasten the toilet back down. If it's hardened plastic stuck to the side, then drain out the water and scrape it off. If you're not handy with plumbing then call a plumber. He can lift the toilet or tell you how to drain the bowel.

Or........what is the problem?

Anything that would dissolve plastic would be toxic to use and would ruin the porcelaine too. can't spell it. lol