Its a total butt pain right?! I've been using it since week 2 and still get the odd block but can get it unblocked now. Best not to suck it yourself really but go up to a 3, kitty has coped with a 3 since 4 weeks due to the thickness, also you need to heat your water first and to a nice warm temp, THEN add the formula and watch the formula get eaten by the water before you shale for at least 15 seconds vigourously. Also I shake again a few times throughout and then roll the bottle to burst the bubbles, this has been fine and kitty is no longer a gassy little trumper!
It is worth it in the long run tho as it's helped us no end and remember it takes a good 2 weeks to start to really work.
If you still clog up then release the pressure by undoing the teet a little, tighten and shake whilst squeezing, this more often then not uncloggs, you'll see drips flying everywhere lol! If still blocked wash hands and squeeze the teet then do the step above again and if needs be pour boiling water over the feet the re-sterilise.
But mainly use a 3 to stop it all together! X