Record which fixtures are affected
One sink behaving differently from several fixtures changes the diagnostic picture.
Notice recurrence
A problem that repeatedly returns after superficial clearing needs better diagnosis.
Avoid escalating chemical mixtures
Different drain products can react dangerously; follow labels and do not combine cleaners.
Professional scope may include diagnosis before repair
The useful question is what is restricting flow and where, not which aggressive method can be tried next.
Safety boundary. General planning information only. Do not open, dismantle or work on hazardous electrical, gas, structural, fire-protection or contaminated-water systems unless you are appropriately qualified and authorized.