If one had 1 litre of around 15 to 20% Phosphorus Acid with less than 5% Tensides within, is there a way to divide the h3po4 from the tensides so one could use it in meth production, for example?
(only hypothetical of course )
I know this sounds like a Stimulant question, but it's also on Chemicals and Equipment, so i hope this forum is the right place to post ...

Very, very difficult in my opinion and not worth the effort. Can't you get any other source of H3PO4? If you can't find it 85%, find the rust cleaners containing only diluted phosphoric acid, some with a little methanol added. See the thread:

Post 512651

(fnord: "isolating phosphoric acid", Newbee Forum).

I'm pretty sure he's trying to separate H₃PO₃ (phosphorous acid) not H₃PO₄ (phosphoric acid).