Sewage compost mulch pit/tree bog?

I have a challenge that I hope you all can contribute to a solution, so here's my issue: I have an apartment in an old converted chicken coop that contains a toilet and shower. There is no evidence of a septic tank or formal septic plumbing, and the toilet is NOT a composting toilet.  There's a good chance that the previous owners just buried a 50 gallon drum in the ground and called it a day, which had me wondering...since I have limited funds and want to use the materials already available (current toilet), what would be the best way to design a blackwater tree bog/mulch pit so I can rent this apartment and generate some income. (And know that my township cares not about things of this nature. It's like the wild west out here - and I just want to do right by the land).

There are things you can do cheaply and things that you really should invest the money to do right.  Anything having to do with sewage is something worth investing the money to do right.

A 55 gallon drum will very quickly fill up and then you'll have a mess on your hands.  If that's what the previous owners "installed", it will not be sufficient for any sort of long-term inhabitant.  You're looking at a gross, stinky mess down the road.  Down through the years, I've seen all sorts of jenky homespun septic systems that were a nightmare: stinky and dangerous.

A composting toilet would be much much less expensive than a septic system, and the added bonus would be that you wouldn't be wasting all that water.  If someone is cool with living in a converted chicken coop, hopefully they'd be cool with giving the old composting toilet a crank every other day.  

If it were me, I'd bite the bullet and invest the money in a proper septic system.  Yes, it'll cost you $4000 or more, but once it's in (if large enough and installed correctly), you'll never have to worry about it again in your lifetime.  You can run the leach line from the septic system out to the trees you mentioned -- double duty.

Assuming you could take $100 a month from what you charge in the monthly rent x 12 months ($1200 a year), x 4 years = $4800.  Paid for in a short time, and peace of mind forever.  That's worth something to me.  

The area around the coop is heavily forested with decent sized trees, and I don't want compact their root systems. A formalized system is beyond the wallet. I have a macerator pump I salvaged from a friend's basement bathroom remodel, so I plan on putting that to use in combination with the tree bog/mulch pit. At no point will any materials be exposed to the air, and the amount of use this will get will be nominal (hoping to rent as an AirBNB - which would limit my rentals with a composting toilet option).

Adding compositing worms into the mulch load was also a thought, along with biochar. Not sure on the chemistry with all that, but hopefully someone will chime in who knows all that.