At today’s inspection of a 1938 house I found a a wood septic tank. I have no idea if the wood is framing to hold up stone, block or concrete walls but the interior of the tank (as far as I can see) is wood framed. Not something you see everyday. System was failed as the effluent level was 2 inches above the laterals leaving the distribution box. House was on a very small in-town lot; tank was partially under a rear addition. Not going to be a very easy or cheap replacement. Sorry about the pics not being “straight”…hanging the camera down inside the tank is always a little tricky.