When connecting threaded pipes, it is advised that some type of sealant (pipe dope, Teflon tape) is used on the threads. Is this to prevent leaking or to make the joint easier to disconnect? Also why not just use good old silicon caulk?
Pipe dope is used as a sealant. Once it is applied and left to set up it is very hard to break the joint. I don't know anyone who has tried silicone but I don't think I would try it. If it fails you don't want to replumb something. Threaded pipe has a way of not threading back exactly the same once it has been torqued the first time. I would stick with pipe dope. Specifically Loctite 567.
Teflon tape can also be used, but I have had many more leaks using this as compared to pipe sealant. In my experience, 4 wraps of teflon tape are required to ensure a tight seal. Pipe sealant is somewhat messy to use, but after the joint is completed, just wipe off the excess with a paper towel. Do not allow the sealant to get inside the pipe.
Pipe dope is used as a sealant. It is also used as a lubricant during assembly. Once it sets up it is very hard to disassemble. I don't know if you can use silicone or not but I wouldn't try it. Pipe dope is much thicker.