I clean septics in NH. The tank and outlet filters in a tank with a softener attached to it will be clogged with a black goo, that is the minerals being flushed from softener along with the dissolved salt. The newer sytems,Presby,Enviroseptic,etc. can take a beating from softeners and medicines peopletake daily. It will clog the membrane[fabric] around the tubes,especially if the fields aren't vented. My softener goes to a seperate drain. It is allowed in NH,may have to have a designer advise you where to locate it. The septic designs can have disclaimers that prohibit softener,garbage disposal or jacuzzi tubs from draining into septic. That way the septic designer doesn't take the blame if a system has an early failure. The newer systems may not last 20-30 years like the older stone systems. The membrane acts like a filter. In theory the effluent water is suppose to be cleaner leaving the bottom of the membrane then the effluent draining thru stone into sand. plowking