You can top fill any KF. On the V2, 3.1, etc, remove the top cap. Cover the air intake(s) with fingers, fill to about the middle of the threads where the top cap goes. Get the top started on, invert (back to right side up) and finish tightening the top. I've not found much difference on when after you turn it back rightside, btw. Take a couple draws to re-establish the vacuum, done.
you can also get a bell cap for it with top fill. You lose some ml of space but you can easily fill it right back up again. no tools required.You can top fill any KF. On the V2, 3.1, etc, remove the top cap. Cover the air intake(s) with fingers, fill to about the middle of the threads where the top cap goes. Get the top started on, invert (back to right side up) and finish tightening the top. I've not found much difference on when after you turn it back rightside, btw. Take a couple draws to re-establish the vacuum, done.