OP: Do you actually have an auto battery? It seems most of the responses to you have assumed so simply because you mentioned the Volt. Regardless, I'll give you the gamut of answers to try and help you out.
IF your batteries are automatic, there are no atomizers which will work out of the box. A 901 will fit the threads, yes, but it uses a different means of airflow than a "sealed" 808 to activate the battery and heat the coil. A 510 atomizer will work with an unsealed 510-808 adapter, and is your best bet for dripping on a Volt automatic. In a pinch, you can also modify a Volt cartomizer (or any other center coil cartomizer) for use as a dripping atomizer, but it will leak like a sieve. Simply soak the cartomizer in water and then remove the polyfill leaving the center air tube intact. No more than 2 drops in a modified carto in my experience; any less and you'll immediately get a dry hit, more and it will flood the coil and be worthless until you blow it out. As mentioned, any standard 510/901 drip tip will work just fine. S.I. even sells rubber "comfort tips" that will work well, though I find the rubber alters the taste.
And yes, too much fluid in a "sealed" battery can gunk up the vacuum switch. But it literally requires a flood of liquid seeping in. If you're careful, and clean the threads of your battery and carto every couple of hits, you should have no problems. There are even ways to fix a gunked up switch should it occur, which most people either never knew about or have forgotten how.
IF you have a manual battery, a 901 atomizer will work just fine with no adapters or modding needed. I've used both 901 and 510 atties, as well as modded cartos, and I prefer the flavor of a 901. It just feels cleaner, even though I no longer drip. Manual batteries can also be ruined by too much juice seeping in, though it is extremely rare. Again, this can be fixed, but the easiest solution is regular cleaning of everything.
Clearos are another good option for testing juices, but an atomizer and a good Delrin or stainless steel drip tip will give you a much stronger throat hit and better flavor.
The best method for cleaning cartomizers in my experience is to actually disassemble them completely and give everything a good soak in alcohol. It isn't very easy to do with the smaller cartos that S.I. sells, but it can be done. Some have also suggested to fill an old cartomizer with straight PG and vape it dry, but I've never tried that.
Good luck!
