Steve Barker LT wrote:

Ahem! There wouldn't be any scum in a tank that is just pumped.

Of course not.

They'll refill in 2 or 3 days and there won't be any significant scum in that time.

A family of 4 with a 1500 gallon tank would take more than 2 or 3 days
to refill the tank. After a week of showers and laundry and
dishwashing there will be scum.

Is this going to single-handedly ruin your drain field? Of course not.
But if you pump your tank every year, over time it will contribute to
drain field failure. Install a downpipe if you pump frequently.