+1 for the Smoktech DCT (polypropylene model only, the polycarb models that are clear do leak) in 3.5 ml for the slimmer ego batteries.
The Valley View Vapes
tanks are great tanks, I have 3, however these are big and heavy for an ego battery in my opinion, very top heavy. The silicone gommets that these come with are a pain to fill and replace a carto; filling requires using a needle and syringe between the grommet and tank/or/carto. Pay more for the optional aluminum caps and you'll be a happier camper.
A slimmer pyrex tank alternative is the OCD tanks from IBTanked. The slimmer tanks he has are 19mm wide, much more fitting for an ego battery. You can get one as cheap as $21 before tax and shipping, not a better deal anywhere. Last pic below is a slim IBTanked on a Twist.


