[Ballistic]

Hi guys, can anyone help me out here?
I'm making a 1 molar solution of Sodium Hydroxide from drain cleaner. It's an old tub that reads 99-100% w/w Sodium Hydroxide.
To me, that means there's no fillers or coatings or non-caking agents.
However, the finished solution in distilled water is cloudy, the cloud then settles to leave a sediment.
I'm currently having a go at filtering and that seems to work, although I don't know, with the paper I'm using if another sediment will form.
Am I right in saying pure Sodium Hydroxide shouldn't do this as it's very soluble in water?
thanks in advance!

[Hunter2]

Pure sodium hydroxide will be dissolved without precipitation. I think a drain cleaner contains some other incredentia. So this cannot be compared. If the sodium hydroxide is old then some is converted to carbonate. If water contain some calcium aprecipitation can take place.

[Ballistic]

Yes, I think it's very old indeed, back of the garage find. I've just made up a 5L batch so I predict we'll see a much bigger layer of precipitate.