We recently had a gulley removed and the remaining drain run capped which had previously served a rarely used double sink unit. I was a bit embarrassed by the amount of fat and grease that had accumulated in the gulley (20 years plus). Washing machine and dish washer and the orginal kitchen sink in the house were served by another drain gulley and run. So be aware of the impact of washing greasy pots etc on your drain run, particularly if the level of waterflow is low.