Even though I don't have children in my home, I prefer to use a bottle with a child-safe lid. With the bottles I use, I know that if I knock over my bottle of lye it will not leak. I know this to be the case because #1, I have tested it, and #2, I have actually knocked a bottle over once or twice. Once, just a couple of days ago, in fact. (safely in my sink, but still it did not leak)
You also need to label it as lye and poisonous.
What I use for storage of my master batch lye is the bottles that Essential Depot's lye comes in because:
1. they are made of HDPE plastic,
2. they have child proof caps,
3. they are already labeled appropriately for the contents*, and
4. they are the perfect size for my hands and not too heavy for me to lift and pour when full.
* But I still add additional labeling information to include the following:
Masterbatch 50% Lye Concentration
date made
amount in solution (which I change as I use it) - because I like to keep tract of how much I have left
On the bottom of the container I have the weight of the container, so I can deduct that from the weight of the bottle as I do my calculations.
I use masking tape and a Permanent Marker to add the additional labeling information on the bottles and when I make new batches, remove the old tape, wash out the bottle with plain water and allow to dry before re-filling with new lye solution.
For safety I still keep my masterbatch lye bottles inside another lye-safe plastic bucket just in case something unforeseen happens and to ensure that I have a doubly safe method of transporting it from my storage area to my soaping area. Granted, for me that is only about a 6 meters away from my kitchen sink, but it makes me feel that I am being as safe as possible.