Thiourea easily decomposes to form sulfide ion and is therefore considered a sulfide toner. It has the advantage that it doesn't smell as bad.
This formula produces results similar to Kodak Brown Toner.
Distilled water 750 ml
Sodium polysulfide, 30% soln 25.0 ml
Sodium carbonate, monohydrate 2.4 g
Water to male 1.0 l
Use full strength and tone for 15 to 20 min at 20 C. After toning place the print in a 10% soln of sodium sulfite to stop toning and then wash to remove any yellow stain.
Some people claim that different formula sulfide toners produce slightly different brown colors. If a certain brown tone is critical then you might have to try several formulas.
There are also hypo-alum toners such as Ilford IT-2. They are easy to make and work better as they age. The toning is slow but can be hastened by heating the bath.