When it comes to handling the double team there are many different techniques, but few of them are actually effective. I am not a fan of dropping your knee ( I believe that gives you a higher chance of injury), and I don't agree with dropping down and creating a pile. Defensive lineman are athletes too and this techniques does nothing but take you out of the play. the way I was taught when I was playing is to fight off the double team and stay in your gap.
Remember on the field your hips are padded so why not use them as a weapon to fight off the double team.
Basic Double Team Drill
Attack the pad, when you feel the double team coming throw your hips at the lineman and position your self in your gap
Advance Double Team Drill
In this drill we are using the hoop to help you with body position and to help you understand, as you are fighting off the Offensive Lineman you still need to squeeze in your gap and fight up field. Once you have reached a certain point you want to shed your man and snap your head in the gap.
Fighting the double team is tough and you might not win every down but this is the best way to give yourself a fighting chance.