I am designing a bath house with mens/womens bathrooms on either side of a shared wall. The perk test specifies that the drain fields must be 23 inches deep (no deeper). The ground is very level.

With the above:

The elevation of the drain field determines the elevation of the septic tank
The elevation of the septic tank determines the elevation of the toilet flange

How can I plumb to achieve the least distance above the ground? Can someone advise, or send me a link that might provide some answers?

Thanks

Ron

Reguradless you have to have 1/8 per foot of fall on 3" pipes and bigger so do the math from there and messure your republic bend and flange

the elevation of the drain field determines the elevation of the septic tank
The elevation of the septic tank determines the elevation of the toilet flange.
Ya got it all backwards my friend.
First the house rough in goes down and the elevation of the slab is set. Then the elevation of the septic tank is set by the elevation of the slab rough in plus the 1/4" to the foot fall from the house to the septic tank and lastly the drain field elevation is set buy the septic tank elevation plus the fall from the tank to the terminal end of the drain field.
Who told you any different? Did you plan to put the drain field in first and then the septic tank and wait until they're in to prep and grade for the bath house site? Under those conditions I don't think anyone can tell you what height to set the closet flange. Good luck anyhow in whatever you do. Tom