I have to agree with the others on the syringle cap.  I tried using other things for the caps, and in the end, the syringe plastic won.  Sadly, I was using 3 ml syringe caps for my plugs, which had a tendancy to deteriorate and break up into my liquid, looked nasty.  Then I started having wicking issues, either my holes were too big, or too small, even though the previous carto worked perfectly with the same hole.  I ended up giving up on the carto-tanks.  Good luck to you though.