I just now filled my pyrex tank from the top and it just took about a minute. I didn't even use the nipple tip that usually comes on the bottle of juice.
I pulled the top grommet up, poured the juice in, then pressed the grommet back in place. Keeping the drip tip on helps to have a little more height so you can pull the grommet up a little higher without it slipping off the top of the carto. Anyway, it fills just fine without a syringe.
With a syringe, I just pull the grommet up enough to get a tiny hole to insert the syringe.
Since I mentioned the grommets, any chance of getting them in blue like you have for the jumbo tanks? Or better still, black? I dunno, but the red almost looks orange, even pinkish. Kinda girly, you know? LOL