That’s what it says on my quote (swinging check valve). I didn’t know there were two kinds.Flapper valve (sometimes called swinging check valve) is more reliable than a check valve but even they need replaced regularly.
We’ve talked about siphon breaks (hole) a few times but they told me they are noisy so I decided I am not getting one. The sump will be large enough and there will be a swinging check valve.Anti siphon hole and sump large enough to handle the back drain are the best remedy. Make sure that they are on unions to be serviced or replaced if you intend to rely on one.
I sit in front of my tank most of the day so a low level of noise is important for me.
I’m not sure I understand what should be on unions ?