Well pumping out your own septic tank and discharging on your property is illegal. So .... you have to understand what your doing , be careful and sneaky. First thing septic sludge is not very sludgie or thick. Yes the solids settled in the first compartment is thicker but pumpable. The problem is the water and doing it safely. First thing what type of soil do you have? What is the value of the perk test. Fast? very fast .,, very slow??
I pumped out my second compartment so low that was down to the connection to first last year. So really pumped out majority of volume, so left about 100 -150 gallon in 1st chamber. Pump flow rate was greater than anticipated so covered a larger area than I thought so was a bit unprepared. I have a very fast perk so liquid volume was gone very soon after I stopped the pump. Left a very thin layer on ground. Again your not dealing with a lot of solids. I ended up having a bonfire which quickly got rid of smell and all the solid residue.
This year have prepared an area that will take almost entire volume. Will check after a couple of minutes to check how fast draining and will turnoff pump if required. Haven't decide if will burn or just cover with soil with a couple of shovel fulls of composted cow manure that is full of red wigglers .
Pumping, If you use a solids handling pump I don't think you will have any issues pumping out everything. Maybe a hose to get the thickest sludge moving and dilute at the bottom of the 1st chamber. Also to get the bit in the corners. If want to use conventional pump then could use an educator but then have a lot more water to deal with.
Overall what are you doing that is different than the septic field ? I'm putting the fluid right beside the end of my field at almost the same elevation. My pipes are about 14" -16" below grade. The difference is that volume is over an hour rather than over 4-5 days. The solids are going to be trapped by the soil in the first couple of inches. As long as those solids are disposed of properly ( burn or cover) not really a difference. The water volume as long as good distance from well or any water course should also be good.
