Washing machine and vent

My father has a drywell that he pumps the washing machine into. This is separate from the septic system. Since it is the only thing on the drain line, other than a trap, does it need a vent line, too? Course, I'm not sure if this is quite legal, either, but has been in use for decades. I'm not sure how different it is from just dumping it into the septic system. Any enlightenment here?

 

Washing machine waste is sewage. It should not go into a dry well. It is and has been poluting your ground water. Even when hooked up to grey water systems, washer waste goes through some filtration. Plus it's diluted with discharges from other, non-detergent bearing fixtures.