I use the condom (cap over the breathing end) method for refilling, so the tight cap is fine/GOOD, tbh on my other model with the rubber one, it moves around too much, especially sliding inside the tube leavinng me with a sharp uncomfortable edge. I did experience the draw issue with the extra filter (but I just poked it aside).
BTW the Hendu cartos are my absolute favorite; I really get bugged by stickers on my carto, sometimes too long, and my princess lips cant stand the edge of the sticker lengthwise either so I always keep turning the thing to avoid the ridge =P