I generally remove the drip tip when using the fill screw and I fill it by unscrewing the entire top and just pouring it in the tank.
For me, flooding occurs when I screw the top back on with the fill screw attached. Pressure builds up and I end up pushing the juice into the carto while screwing the top on. Easy solution, I leave the fill screw out giving the air somewhere to escape.
If you watch your carto you can see the filler getting soaked during the process. (with fill screw attached).
If you fill with a needle in the fill hole, well, that's a small hole and displaced air may have a problem escaping past your needle, creating pressure that causes flooding.
The 510 attachnment does not have side holes, just a center hole. Some mods, like certain lava tubes, have a slim center pin that can plug that up.