I can't remember where I read about this but it is certainly a great tip that could save you lots of frustration and money.
If you have a clogged sink or tub or toilet, put in about 1/2 cup of Dawn dish soap straight down to the drain.
Let it sit for about 15 to 20 minutes. Then add 4 or more cups of boiling hot water. The drain should clear.
I tried this with a somewhat clogged toilet, it was not over flowing but it was not flushing completely, only the water was sort of going down. I added the Dawn and let it sit for 15 to 20 minutes, added about 4 cups of the hottest tap water, boiling would probably be better, waited another 5-10 minutes and flushed. It whooshed right down and the toilet was clean as could be.
Apparently Dawn is the secret weapon of plumbers.
This is not a paid for review, just my own experience.