I know I am new here, but I strongly agree with the 3ml trick! The plastic is much more durable, its a tight fit, but that just means alot better leak protection.
My Bro-InLaw works at a gas station, so he always has his entire e-cig in his pocket (Box Mod with On/Off Switch + CE2-X XL's with Modded 3ml tubes) His Tubes never break, and I keep mine in my jacket pocket all the time, and same results.
With the regular stock tube on the Rev. 2 of the CE2, the tube cracked within 3 days on me, then my bro-inlaw and myself both did the 3ml tube replacement, And I wont use anything else for a "stock" tube replacement.
Here is how big the 3ml tube is in thickness compaired to a stock tube:
I took this pic with my LCD screen in the background since im taking these pics with my phone, but you get an idea of how much thicker the plastic is. Its not hard to fit the plastic over the 510 connector at the bottom at all, and its nice and tight!
And as drewk302 said, you can get bigger to do a tank mod.
These are just 2 examples, and there are many more threads about tanks around the forums.
First is my BIG tank on an CE2 XL, 2nd one is my "mini" tank on a CE2 XL, then the 3rd is a stock sized CE2 with the 3ml tube replacement
EDIT: you can get the 3ml syringe from walgreens for $0.25 each, and if you are using it to replace the tube of a stock sized CE2 (not the XL) then each Syringe can give you 2 replacement tubes after you cut them to size.