Put a dish tub in your sink, use that to wash your dishes and then you can dump the dish tub of water into the drain.
Or, just use your sink and dump your grey water at a real dump station when necessary.
One thing folks forget when wanting to dump their grey tanks in these "not made for RV dumping" spots is that your grey water and black water dump from the SAME pipe (and the same hoses). Unless you're scrubbing that pipe (and hose) thoroughly with disinfectant, there WILL be residue left on the inside surfaces - even if you're "rinsing" the pipe (and hoses) with the grey water after dumping the black water. Therefore the entire system IS contaminated. That is why there are rules against RVs dumping grey water on the ground when folks are allowed dump dish washing water on the ground.