Water leak from under bathroom sink

[Old-Biscuit]

NEVER hookup to flush connection unless you are actually flushing black tank.


Slow leaks/inadvertently get turned on.......black tank overfills...leak out toilet OR blows out roof vent (fountain of poo)


Those anti-siphon vacuum breakers require at minimum 40 psi in order to lift disc & seal openin at top to atmosphere.
High pressure will also cause them to leak....above 65 psi


Yours maybe OK........leaked because of the low pressure leak thru from that 'WYE' connector







***You mentioned being in a site that was slanted/off level
Hope you are NOT running fridge (if it is an absorption fridge)
If it IS......you ARE causing damage.