DWV: Clothes Washer and Utility Sink
I would suggest spending some time reading the code applicable to your area - for me, that's the IPC (with a few local changes) and it's easily available on-line.
Pretty much the entire point of vents (that pipe in the middle that goes up) is to prevent siphoning of traps. So, no, that should not be subject to siphoning the trap when using the other fixture, since there appears to be an adequate vent. That's a perfectly acceptable arrangement - well, it might be missing a required clean-out, at least under UPC, as I understand UPC (but I don't spend a lot of effort on it since it does not apply to me.) What code section makes you think it's not?
That is a &quot;Double-Tee&quot; or &quot;Cross&quot; - it's not particularly superior to using a pair of Tees. At toilet scale it can even be a problem (and you'll find that in the codes if you read them.)