School basin installations

Attachment Deleted..got this leaking sack of shit to sort out next week. Everything is rigid, iso don't work, jobs at a school. Can't free trap from slotted waste, I've had a go at removing slotted waste renewing washer on trap,but still leaking. Bought new trap and slotted waste give that a  go next week. all the toilets in the school have been fitted with the washer against the metal support bracket then tighten up with the back nut. Why! I seal up put a poly washer on then a metal back nut and then put it on the metal bracket then connect the trap. Has anyone else seen it done this way,or is it a bad installation?  and the toilets are smelly,bloody kids,endfeed not happy