The aircraft has two toilet and waste water tanks.
This is what stopped the toilets working, the full sensors shut the toilets down when they get activated.
The toilets are grouped for the waste tanks, hence they shut down as they did.
It's always been a problem with the 767, normally a pre charge is put into each tank after it is emptied.
On longhaul the pre charge is not carried out, this might have been missed or the tanks not emptied fully.