Is there anything that I should definitely not put into the system?

Since your treatment system is a living culture, you should avoid flushing or draining toxic materials into the system such as paint, household chemicals and antibiotic medicines as they can harm the natural bacterial action that is present.  Other items to avoid flushing into the system include bulky or non-biodegradable materials in general such as sanitary napkins, paper towels and cigarette butts.   Coffee grounds and excessive cooking grease are not helpful to efficient system processing and should be disposed of through your compost/recycle/solid waste stream instead of though your treatment system.