I have a couple of the Mega attys and carts that I haven't used yet but when I do, I am going to go with the blue foam mod that I saw here a couple of months ago. Wish I could find it again, but the fellow said it works great. Basically what he did was fill the cart with
juice, leaving the original filler in place. Compress it down until the
juice begins to ooze to the top. Then he added a square of blue foam on top of the original filler. Press the blue foam down to soak up some juice or add drops to it so it isn't dry. With a new atty, naturally you want to prime the atty with a few drops.
I will probably end up removing all the polyfil and replacing it with blue foam if that doesn't work. I just haven't figured out how to pack it in the cart yet to get the correct amount of fill and compression. Maybe roll it? Its gonna have to fit the cart opening completely to keep it from leaking.
Anyway, there is a specific blue foam that is recommended. Its available at most Petsmart stores. Walmart did not have it.
It is Marineland brand, Rite size U. Comes in a pack of 3. The other sizes are a completely different type of foam, so it has to be Rite size U. It is in a sleeve configuration. Just cut open down one side and unfold it. Wash it well with hot/warm water and dish soap to remove unwanted flavors and the antibacterial agent on it. Rinse well and let dry. One pack should last a long time. Cost: 7 to 9 bucks.
I use this stuff in all my regular carts too only sans polyfil.
http://www.e-cigarette-forum.com/forum/cartridge-mods/117465-polly-blue-mega-ego-carts.html
Edit: Found it in the cart mod threads