I just had occasion to use the THC fill adapter for the second time. The first time was a bit of a struggle, as those that have them know, they're quite tight in fit to the inside of the cart. They have to be, if the cart backs up in loading, it's going to leak at the junction. Last time I managed with a little cussing to get it in and seated. This time, no way. Turning the mouth of the cart in finger tips showed it slightly out of round (not uncommon), the mouth of the adapter was more round, but had a ding on it that was clearly an issue. A minute or so with a flat file put a very narrow (maybe .020 wide?) bevel on the lip, smoothing it out in the process. Just enough to deal with the out of round situation. Works great now, no struggles in 8 or so carts I tried it in. A little wiggle to center it up and get it started straight and 'Bob's your uncle' as the Brits say. IMO worth considering.
Until now I've been very happy with my modified number 10 tip (the one Planet Vape used to ship (before the official funnel)). With sharp scissors I trimmed 1/18 or so from the small end so it was a closer match to the cart. I suspect a different tip (#11 or 12?) would work without trimming. I then put the shaft of a punch in the end (you could use a round screwdriver shaft, perhaps a bit easier) and used it to flare the mouth out parallel for 1/8 or so back. A straight tube bit on the end that barely slips into the cart like the THC adapter does but being thin it's easy to insert. It also stays place well, and being thin is faster (more responsive) to heat when melting down. I plug the center tube with a toothpick when doing this, cutting it off short to keep it out of the way.
I'll give the factory unit a few more tries, but IMO the modified funnel is easier to control when filling.
OF