If you have a 300td (wagon) it is not a big socket, It is a big hex nut (no need to diconnect a fuel line on a wagon). I can't remember the size (do a search) but run the tank to reserve plus some. there is still alot in there. Pull the strainer and pour the diesel back in to flush it with the strainer still off. clean the strainer and replace the gasket (if so inclined) and you should be good to go.