I have 500 ft of drainfield that has stopped working.I didn't maintain it over the years.It worked for twenty-five years without a problem.I have two questions.One the distribution boxes and drainfield are ten feet apart.I am going to replace 300 ft right now.Do I need to clean out the original drainfield trenches and put in new drainfield,rock in the old trenches or make new trenches between the old trenches.Two,What size rock do I order to use in the trenches.Thanks.