Yes, it can give off intense heat.
Yes, sometimes enough heat to melt parts of plastic piping.
Yep it so is
They share the same drain and it is becoming clogged. Drain cleaner in both drains should help.
physical change
It may clean out some clogged materials, but in general , household drain cleaner is junk that should be avoided. You achieve more by mechanical cleaning with augers and rods.
Use a snake and unclog the drain PROPERLY. Do it quick before everything is eaten away on the tub and drain.
The drains can get clogged and back up into each other. You can try plunging the drain to clear it, use drain cleaner or call a plumber.
If your bathtub or shower drain is clogged, chances are it's clogged with hair and almost any drain cleaner sold in stores will dissolve a hair blockage. Follow instructions on the bottle. If it's your kitchen drain, there are products to clean garbage disposals that will dissolve most food products. Again follow directions on the bottle and use hot water.
Yes, it is, if you find if useful, use it. I usually favour a springy drain cleaner as it can get round bends easily. Anything that works - -
The drain going out is clogged. Both sides share the same drain and water seeks it's own level so it comes up in the other side. Put some drain cleaner down the drain.
If it is an alkali drain cleaner, you can add acidic materials in the drain cleaner such as lemons, If it is an acidic drain (less common) cleaner, you can add alkali materials such as toothpaste, soap
Water won't drain from shower. Either trap or shower drain line is clogged.