Wow! Talk about a literary mess...I personally do not use the term 'sealant' for PVC or for silicone. My language is limited to PVC GLUE and SILICONE RUBBER due to the local trade. I get the feeling that some of the posts here use the word 'sealant' interchangably for both PVC glue and silicone rubber, but I may be translating the posts wrong...
Silicone Rubber is the wrong thing entirely for slip (or socket) fittings. It is ok for low or no pressure threaded fittings. For high pressure applications, you can not beat DodgeFreak's recommendation of teflon tape w/ pipe dope. Myself, I prefer the teflon dope over the clay. I have just had better results with it.
Silicone Rubber comes in different grades for different applications. The cheapest silicone rubbers are unsuitable for plumbing but the higher end products will hold 50 psi if allowed to cure over night. To tell the difference between silicones takes experience in feeling the texture/thickness of the uncured product. A good quality silicone is much thicker than the bargain bin silicones. Boss products, GE 1200 series, and any aquarium silicone is good enough for threaded plumbing fittings. However, siliconed parts do not clean up after dissassembly like teflon tape and pipe dope.
Teflon tape by itself is a craps shoot if you do not have experience with it. Keep in mind that this is also the stuff used in assembling galvanized pipe (or simply 'galvanized'). PVC requires different instructions, and galvanized pipe has been around much longer. The manufactures it seems, are pretty lazy in that they always give the directions for galvanized but rarely for PVC. I have run into many tradesmen and old timers that also assemble PVC like galvanized. If your helper insists on three wraps of tape and then a good wrenching until all of the threads are no longer visible...take his beer away and send him home. Over tightening is the leading cause of broken parts, not only during assembly but also down the road. Both galvanized and PVC have tapered threads but PVC is still plastic and has its limitations. Instead of three wraps, give it 7-10 tight wraps and then compress them by "screwing" the part into a clenched hand. When joining the two parts, tighten them hand tight (as tight as you can possibly get them by hand) and then with a wrench give them an additional 1 1/2 to 2 turns. More won't cause the end of the world, just resist the urge to wrench it down to the bottom of the threads.
If you feel you may need to dissassemble your work in the future, you can use compression fittings, unions, and threaded fittings. For frequent dissassembly, you should use unions but they are the most costly option (though well worth it).
The LifeGuard silicone grease can be had for around a buck from your local swimming pool store (if you live in the South). Any brand will do the trick and can be found in your Home Depots pool section and/or plumbing isle. Vaseline, etc. can do funky things to black rubber products however many newer synthetic rubbers are unaffected by petroleum greases; they can make a mess of your tanks rather quickly though.