Can I use this for cold process soap making?
Yes it is perfect. 100% lye. Nothing else in it. Easily dissolves. I made beautiful soaps. by Dee Cs
Yes, cold process soap making uses a pot of oils and an alkali (lye) to convert them to soap in a process called saponification. It’s wonderful on the skin. by Lynetta Laws
Yes, I just did. by Taozi

Will this work for toilets? The instructions advise you to use hot water, which you do not find in a toilet. 
One of the other reviewers said it worked well. That person added hot water to the toilet after boiling on the stove. by Sunshineluv7

Can this be used on a pop-up drain in a bathroom sink? How would you do that?
Yes, Patricia, most of the pop-up drain systems that I’ve worked with can be screwed up and off the stem. So, the silver round “top” screws off generally. Once off, simply pour the desired amount of Lye down the drain and flush. That should do it; unless you have a strange older pop-up system. Most of the ones that I work with are around 35 years old or a bit older. Simply push the pop-up in the up position then turn the head counter clockwise and that should work. Good luck with it!!! by lonelyboy267

Is it safe for bathtub brass drain and pipe? 
All the reviews I read on this said it was ok, and that was my experience. The shower drain had a metal cover. Since the product warns DO NOT bring into contact with aluminum, I removed the cover to the drain. I just didn’t have a clue what the cover was made of. In the sink, I remove the stopper that sits inside the drain for both that reason, and I wanted to be able to pour the lye straight into the drain. I ran hot water down both for about 5 minutes. Then I used paper towels to soak and wipe up any water or dampness around the drain. I’m not sure I emphasized it enough, but the only… by Miztahchipz

Does it work to get rid of sewer flies 
I have never had this problem, but after reading about them, I am inclined to say YES, that it will take care of the flies in two ways. First, lye is a chemical that burns your skin if you come in contact with it so it’s pretty powerful stuff. I doubt any fly eggs or flies that come in contact with the stuff will survive. More importantly though, the Lye will totally wipe out any slime or gunk in the drain which is what the fly uses to as it’s nesting ground.  by Derek

Is this pure Sodium Hydroxide?
Yes. I bought mine for soap making. by Kathleen Fyock

Can it open drain in bathroom sink locked by hair?
It took care of the hair in my shower; I’m sure it would work fine in a sink. by lux et lex
It worked perfectly in mine. by sadra
I usually just pour about half the bottle into my drain and run hot water through. my slow running drain always clears out quickly. It says to wear protective gear but I don’t. I don’t touch the lye, just the bottle. by Kabuki

I have a very slow draining shower and typical Drano/Liquid Plumber does is not effective. How much of this container should I use at a time?
I’d use half of this container to start. You might need to use the whole thing on one drain depending on how clogged. Also, make sure nothing is stuck down there and preventing the water from draining. by Franxswife

What about the pipes like PVC?
The pipes I have are PVC and they seemed fine. Just made sure to run the water for a minute or so to wash all of the lye away.
I have PVC pipes and has not damaged mine. by Billy
ComStar says that ComStar Pure Lye® can be used in all types of pipes without harming them.

My house is about 70 years old, and I do not know what kind of pipes we have. Is this product safe to use on my bathroom sink?
There’s no way to know for 100% sure since you don’t know what kind of pipes you have. But this stuff is waaaaaaaay nicer to your pipes than drain-o is. So if you’ve used commercial drain solutions in the past, this should be fine. by Mariko

ComStar says that ComStar Pure Lye® can be used on a regular basis and is recommended for monthly drain cleaning maintenance.

Can I use this in my garbage disposal?
Yes, I used it in my disposal with good results and it did not harm anything. by Mr.E
Yes. Run some hot water first, then use the Lye. I’d probably run the water for a minute or so after it’s done unclogging the pipe too. As long as you aren’t planning on eating out of the garbage disposal, it’s perfectly safe! by Arthur Dayne

ComStar says ComStar Pure Lye® is safe to use in garbage disposals. Make sure to remove the case of the blockage and then let the ComStar Pure Lye® solution stay in the disposal unit for approximately 20 minutes. Reapply as necessary.

Can I use this in a slow running basement floor drain?
ComStar says ComStar Pure Lye® can be used in any and all types of waste pipe drain systems. Just follow the instructions on the bottles label.

Will this go through standing water and kill roots?
ComStar says the ComStar Pure Lye® can be used to eliminate root growth in septic and sewer lines. It can be flushed down a toilet for easy application. The State of Massachusetts prohibits the use of various types of products to be used in septic systems.

Is this food grade lye? Can it be used for baking pretzels?
ComStar Pure Lye® is food grade and can be used in this application.

Is there any other active ingredients or chemicals besides lye in this? Mar 1, 2014
It is all pure lye. No other additions, dyes or fillers.

Many of the answers above have been provided by real customers who have lent their opinions on online shopping channels. We have given them credit by way of their screen names in italics.