SN is Sodium Nitrite.
It's usually used in kitchen for meat and fish, to make the appearance more pink and cured meat. It's poisonous if swallowed in high doses. 5mg-30mg.
You need dsmo (unregulated) and sodium nitrite (unregulated as well).
You pour 100ml of dsmo in a glass. And then add 15-20mg of SN. You mix it without a spoon, swirl your glass, so the SN melt in the dsmo. Then it's ready to drink. It'll taste like very strong garlic, even spicy.
In PPeH report, it's apparently painless (SN used alone) , drowsy after 3min, unconscious after 12min, and death occur in 34min. But some reports says it's painful.
Hence why using dsmo, it accelerate the process. Xerxes made a topic or two of his experiments, you should read them.