Is there any valid reason whatsoever that anyone would install a brick septic tank in the first place, unless it is pre-1950 or so?

Also, is there any valid reason someone would opt to not replace a brick septic tank when re-doing all the lateral lines and distribution boxes?

I have a customer who has contacted the prior owner of the property who claimed to have put in the system in 1999. Checking the permit record revealed that the "existing septic tank" was used, and the owner stated it was "brick". Permit records show the drawing and specifications for the lateral lines, which look okay. My concern is that the service life of any brick septic tank would be very short, in the 7-10 year range maximum, and surely the "brick septic" tank was installed ages ago... the building was built in 1925 and originally had outhouses. Unknown on the original septic installation date. My concern is that the existing tank could be leaking profusely into the soil, and it is located right behind the basement wall. There has been water leaking and a strange buildup of mud and black colored stuff. No smell, no oil, just coloration. Maybe from the cistern which is also right behind the basement wall...

I told them to replace the septic tank with a modern solution and have a contractor mark off and verify the existence of the laterals illustrated on the drawing.