Our sinks started backing up about the same time we put bottompaint over the waterline stripe.
We also installed a macerator on the galley sink drain which worked well for a while but then started having trouble pushing drain water against the backpressure of the seawater. The initial workaround was to tee the outlet into the deck drain at the water line
which worked fine but as someone else noted the noise of the pump
is very noticable.
I then tried a long length of outlet hose in a loop up near the diesel deck fill and back down to the sink drain through-hull. This fixed the backpressure and the noise problems and has been working for a few years now.
C37 yawl #22