Plumbing advice re: reliability of pvc unions

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I'm going to re-plumb my tank after many years. I wanted to know people's experience with unions.

So far I have only had unions on drain lines which are over the sump, in case of a leak it would drip into the sump. None have leaked though.

I am looking at adding a couple of unions to the return line for ease of access, and these would be in the back of the tank. A leak would be a minor disaster.

Just wondering if people have experience on leaking or non-leaking of return lines which are under pressure.