Hello:

Have done a fair amount of home plumbing type of work, but, surprisingly,
have never had need to use a "union".

Have to run a line from a washing machine water outlet to the machine, and
for various reasons, before I get to the hose itself, I could use a Union in
the rigid section to provide some angularity adjustment, as well as the
removable advantage they provide.

Have looked at them at HD, and frankly they make me very nervous.

What's your experience with these things.
e.g.,

Once you snug them up, do they tend to stay that way ?

Reason i'm asking is that there is no elasticity in the union coupling
itself, so it seems to me that if the threads back off, even a very small
amount, there will be leakage thru the ground and polished seat where the
two pieces actually come together.

Any thoughts on this ?
Safe to use ? Proven in practice pretty well ?

Are there any other types, or brands, besides the HD ones that are perhaps
of better quality ?

Thanks,
Bob