1. if you are adding juice to cartomizers - ALWAYS take the carto off the battery. After adding juice - clean up the threaded end. Then if the carto has a defined center air channel, tilt the open end down into a tissue and puff into the threaded end to clear the air channel. WHILE the battery is still open end down, make a soft point or narrow soft clump of tissue and poke it up into the open carto until it touches the stuffing to get any loose juice. To be even safer, you can put that tissue in right before you tilt it down to do the puff into the threaded end. It will not be the most filled carto but it will be much less likely to leak.
2. Give up Blu. Buy Joye (not a clone) 510 manual instead (and do NOT share chargers - it has the same threading as Blu but Blu is reverse polarity and will fry a 510 battery with its charger and vice versa.). AZSMokeFree has a nice roomy PCC for 510 that works with the manuals (2 battery slot one of which is for charging and 6 other slots). You can use Blu cartos on it or use any standard resistance 510 cartos on it (most are blanks and the most popular are Boge - you would use the standard resistance which is around 3 ohms)