You are right ^^^ it is sulphuric acid and formaldehyde. I wouldn't use a tissue to wipe away the reagent, I test on a ceramic plate (that I only use for testing, just to be safe), then very carefully wash the reagent down the drain in my stainless steel kitchen sink. I then wash the plate with dish liquid immediately. Keep in mind that testing on plastic is iffy, the reagent could easily eat a hole into plastic items.
Testing kits are DANGEROUS. Treat them as such.