If you need to unclog a drain that's slow or not draining at all, you have two options. You can do it yourself or call the plumber. Calling the plumber (me) isn't always convenient. And I do charge for a service call.
Many of my customers have told me that they put boiling water down their slow kitchen or bathroom sink drain, sometimes with baking soda. Where did they come up with that idea? My wife showed me several plumbing advice websites that actually recommend doing that. Well, that's a bad idea for several reasons.
I say needless risk because the answer is obvious-
Hot tap water, that is. Use all the 140 degree water that you want! If a couple of sinks full of 140 degree water don't unclog the drain, then it probably needs to be snaked. At least when you or the plumber puts a cable in the drain, they're not going to get drain chemicals all over themselves.
If you want to run hot water down a drain once a week or even monthly to prevent clogged sink drains, than go for it! It will help keep the pipe walls clear of the solid fats that are a problem in some drains.
I just don't understand the reason why people recommend boiling water to unclog a drain! If you keep your hot water under 140 degrees, use the hottest tap water you have.
Even a lower temperature of hot water will help keep your drain clear. It will just take more of it. If this seems wasteful, just think how much more wasted time and money a trip to the hospital would be. Or how much the repair of a cabinet would cost after it got a load of boiling water when the P-trap failed.