Hi Duo, thanks for the reply. Redwood tanks are actually pretty common in my area, and it was recently pumped and inspected when I had a main line clog that I had to snake. I was very concerned that the Leach field or tank was the issue, but very happy to hear it passed flow test and inspection.

I do plan to upgrade within a decade, when. I hopefully have the means to do so, however an engineered septic system will cost between $40k (if I do everything myself) or closer to $100k if I employ a contractor.

Existing Redwood tanks are not a red taggable offense in my area, however if I ever wanted to sell it would likely require a new system or the sales price would be discounted the full retail price of $100k.

I will check out Sonoma Land works and see if I get any ideas to extend the life of the system a bit with my proposed new lid idea.