To be a really successful singed you must be able to gas your enemies all at ones, or at least as many as possible. This gives the best damage output, at will make this tank build so hardcore, because of your high survivabiltity, and your great damageoutput over time.
When you engage with Singed you should make sure to make them chase you, and also make sure to engage melee targets so you ill be able to fling them, and bring your team an easy kill, by isolating a single target while you keep the rest of the team busy, but also damaging all, or most of them.