Bad starting td5

Hi ,
Posted a thread a couple of weeks ago about my td5 disco having bad starting when the car has been parked up for a few hours . I had black bits in my fuel filter, my local garage told me to run the fuel low so they could remove the tank and flush out, I have run the tank low and the bloody thing is starting first time and running great I have been adding millers fuel Adative,
Anybody got a clue what is going on.


Thanks