I don't know if it is a good idea to dump, say 50 to 100 gallons of sewage into your septic at once through the 3" hose. Maybe it could force solids into the drain field. I have wondered about it for a while since I have a train hooked to my septic also. Forgot to ask the guy that pumps it every three years@ $300.😠
My tank is 1200 gals and visitors have been dumping in it for years at the place in Mohave Valley and I dump there too never a problem yet,here in Scottsdale I don't have a dump yet but working on it so I need the macerator to keep from driving 20 miles and paying $15.00 to dump.We have a 2500 gal septic tank here in Scottsdale and like lots of places in AZ no field lines,they drill a vertical shaft 18in dia x 100 ft deep and fill it with rocks we have 2 of those and it works our tank has a oxygen monitor we watch