There are two things you need to know about those BCC tanks. 1) If you don't fully screw the body of the T3 or ProTank onto the knurled part, you'll get leaks--that connection has to be tight. 2) On the other hand, screwing the knurled part onto the battery shouldn't be too tight, just enough to make contact. If you overtighten, you may raise the center post and your juice will leak. You also have to make sure the thread seal stays above the threading and the other seals are in place but it's just 'eyeing' them mostly.
I own and use all of them--T2, T3, baby T3 and an eVod, with different resistance coils. Never had a leak. Just check the seals and connections carefylly. Especailly with the eVod--that small coil unit needs to screwed into the base tightly--it tends to get loose. Tighten it the first time you use your eVod and every time you clean or refill.