Okay, with the BVC coils, you need to prime them well. You can put *a* drop down in the coil to prime it, too much more would result in flooding, most likely. The main thing is to fill your tank with the new coil in it and let it sit for 15 min--30 minutes. You can do a priming puff now and then, where you inhale through the mouthpiece but don't press the fire button. After you do that about 5--8 times, go ahead and slooowllly raise your wattage, starting about 5 watts, doing some slow, long puffs, then increasing in 5 watt increments until you reach your target wattage (which may be slightly different each time as juices vaporize well at different temperatures, so one juice may do better at a higher (or lower wattage).
As far as washing your coil with the juice you didn't like, you certainly can. People use different methods, I usually rinse mine in very hot water then let it sit overnight in a jar of water. Then, I rinse it again the next day and leave it outside for the day-- I live in AZ where there is very low humidity, though. You can also dry it on low with a blowdryer. That should give you 3--5 days more use out of it, depending.
Your coils aren't going to last forever. With the 0.7 coil, I'd say 1--3 weeks (if you are lucky) depending on your gunking factors: gunking factors include: high VG, low PG juices, very sweet or dark juices, NETs or WTAs, running your coil over its recommended wattage or at high wattage, etc. Sometimes coils just go for various reasons. If a coil is burned, slightly, you can rinse and reuse. If it's totally TORCHED for whatever reason, I would not rinse or reuse.
If your coil goes bad, throw away any remaining eliquid and clean your tank.
Best of luck, hope this helps,
Anna