Throatin a cock down to the nut sac. Especially large cocks where it is a challenge, and you need to open your throat and let it slide deep down. To properly base a cock you need to get your lips in direct contact with the dudes scrotum, and if possible lick his scrotum with your tongue. I've done it many times.
i'll need the guy here with the biggest cock to let me demonstrate the correct way how to base a cock. It made him shoot his load deep down my throat when based his cock again.