They keep doing the same thing because we've tried the airholes in the bottom cap and it creates a whole new set of problems. If you can think up an airflow design for a clearomizer tank, it's probably been tried already, and we've all bought it and hated it. The air holes in the 510 connection has been the preferred air hole location for at least a year now.
If the blockage is in the air holes in the male 510 connection, the only thing you can do is pull your tank's post. Pull it either flush with, or a little bit past the end of the male 510 connection's base. If that doesn't work, you may need to try an adapter. But I don't see why that wouldn't work. unless its not the walls of the female 510 connection's fault and its actually that the airholes in your protank are blocked by juice or crumbs or sand or something. You could try washing your protank out a bit and maybe stick a tooth pick thru the air holes to see if they are blocked. If that doesn't work, then you are simply either flooding your coil to mouth piece tube, or you've got a block in the wick sections. If pulling your post, thinning out the wick, and thinning out your juice do not solve the problem, just send it to me.

I promise I'll have it working and I'll enjoy it thoroughly.
It doesn't sound like a juice flow issue. Unless your juice is overflowing. In that case there is little you can do other than trying to stick an extra piece of cotton into 1 of the wick holes, or plugging one up completely with the broken-off tip of a tooth pick.