I want to clarify that the solution to use silicone 1 would only be for thread to thread PVC connections (for aquarium related plumbing) and not for a union gasket seal leaks. I have been using silicone 1 for over 7 years now to seal PVC thread to thread connection with 100% success and no leaks in two different systems now. The only drawback to silicone 1 is that it must be allowed to cure 12-24hrs before water and pressure can be applied to the plumbing. Teflon tape does work but I find it is the most likely to leak with PVC threads from my experience with aquarium plumbing. The teflon paste is just a mess to work with and the few times I used it there were small pieces of it found in the aquarium system for months after installing the plumbing. When I did maintenance on a pump with the teflon paste it would be a mess to clean and properly seal. While silicone 1 might appear to stick to PVC it can not form a chemical bond and will come off with a light/medium brush.
I was skeptical of using silicone 1 when I was first introduced to the method but its been 100% effective every time I have used it. In my current system I have silicone 1 on PVC threaded fittings for 3/4" returns, 1.5" returns, 2" drain line, and a 4" interconnect line between sumps. While silicone 1 might not be the best solution for every situation I will always put it out there as a simple solution for DIYers. If you have not tired it before it might be worth testing out on a fitting or two as an experiment and see if it works for you.
I was skeptical of using silicone 1 when I was first introduced to the method but its been 100% effective every time I have used it. In my current system I have silicone 1 on PVC threaded fittings for 3/4" returns, 1.5" returns, 2" drain line, and a 4" interconnect line between sumps. While silicone 1 might not be the best solution for every situation I will always put it out there as a simple solution for DIYers. If you have not tired it before it might be worth testing out on a fitting or two as an experiment and see if it works for you.