slow drains need flushing
I have had slow sink drains on my Cat 25 in the past. I blow the lines clean by putting a garden hose in the drain and wrapping a wet cloth around the hose as it enters the drain to stop any water coming back at me. I then have someone turn the hose on and blow the junk out of the lines. Make sure the seq cock is open first! If you have two sinks, plug one up while you clean the other. Also, pour some hot water down the drains once in a while to clear out any grease