I installed septic systems for quite a few years and have seen some weird things people have done with their systems.
Installing an RV sewer dump into a home septic system is very easy. Remember sewer lines should not have quick drops because the water will leave the solids if there are any. Large elevation changes should be made with 90 degree drops. One inch of drop in a one hundred foot line is almost overkill, we always tried for no more than a half inch drop per hundred foot, but that is hard to do using plastic line. Ideally the solids are kept with the liquid and casually float to the septic tank entrance.
Connect your RV dump line into the septic system between the house and septic tank, never into the drain field. Another option is to drop the discharge from you RV directly into the top of the septic tank, preferably before the baffle, but after the baffle will work if that is the only possibility.
A macerator or other grinder will help but is not a requirement. I have installed RV dump lines into several septic systems, used both methods and never had a problem with them. First one I installed was in about the early 1970’s and it is still being used to dump RV septic waste.
The reason I mentioned to install the dump line between the house and septic tank is that I had a dear friend that decided to put in his own septic dump for their RV and hooked it in AFTER the tank and before the leach lines. Needless to say it took us a while digging up the lines and replacing them to get his system working properly again.
If the dump is being used daily or very frequently one needs to make sure to hook in between the house and tank, but for occasional use dumping into the tank after the baffle will work. The baffle in septic tanks is an insurance policy to ensure that the solids go down, not across the top of the liquid in the tank and out into the drain lines.
If dumping in after the baffle, it is a good idea to make sure the waste enters perpendicular, and even to drop the end of the dump down into the water level a few inches. This helps direct the solids to the bottom. I always put the dump about six inches down into the water. NEVER bring waste in AFTER the baffle in a horizontal configuration as the agitation could send the solids across the top of the liquid right into the drain field outlet.
Dumping a forty five gallon tank all at once won’t if the RV dump line is installed as I describe.
When installing new septic systems on lots lots that were big enough for RV’s to be parked I always offered to install an RV dump free of charge and connected it between the house and tank whenever possible. I figured it would save digging up the yard later to install one, and the additional cost of the pipe was minimal.