You can buy the Riva 901 cone - it will screw on the Riva 510 and fit over standard diameter cartos with plenty of carto sticking out (901 cone is much shorter than 510 one. See Liberty-Flights.com if you are in the US, click the 20% off upper left front page, and buy just a Riva 901 cone)
Buy Boge 510 cartos. You can use either the standard ones or the hotter LR ones that use up charge faster. Boges are simple stuffing type cartos and the most popular cartos for 510 threading.
How I fill
Pop out the soft cap with an unbent paperclip in the mouth hole, very careful not to catch stuffing or the wire loop.
Shake and open the eliquid
Hold a bit of tissue on the threaded end hole, tilt the carto, and add 18+ drops per ml of capacity into the stuffing (Boges are about 1ml)
Clean up the threaded end, tilt open end down into tissue, puff into threaded end to clear air channel (Boges have a defined center air channel and I want to see light through that)
Sop up any loose juice above the stuffing
Cap and let it settle - I lay it on different sides for 15-20 minutes to make sure every bit of stuffing gets damp so I won't singe the carto. if you use thicker juice than me (I use 30% Vg or less, I prefer 20%) then you may need to wait much longer. If you use very thick juice you may have to thin it with distilled water or pure grain alcohol (edible - like Everclear).
While
vaping, if the vapor gets a bit light or a bit dry or the carto is getting hotter than normal, I take the carto off the battery and add eliquid. I sometimes use a plastic or delrin drip tip as a mouthpiece on Boge cartos (not to drip into since the juice would head for the central air channel)
