I feel kinda stupid askign this question, but i want to do it right. I just got my 510 in the mail today, along with some juice and empty carts. i want to try out my apple (and other yummy sounding flavors) but im not sure exactly how to fill a cart. i have the regular round tip carts for a 510, i also have some blue foam, if that would work better than the filler the carts come with. it would be really great if someone could help me out... like do i take the filler out and fill it? how many drops do i put in? just the basic stuff i need to know. thank you! thank you! thank you!