Take it for a drive until the engine is hot and you have heating that will melt ya face on hot, that way you know the gearbox is up to temp, let the car idle for a couple of minutes, turn it off, get it up in the air then drain it and leave it draining while you go make a brew. By the time you've done that you should have virtually everything out of the gearbox. Then fill it up from there until it start coming out the filler hole. If you haven't got much in start the car for a couple of seconds then try filling it up again you should be able to get it all in that way. You might be having issues filling your torque converter up