Septic Tank Riser

My tank is a couple feet below grade and many decades old but still in excellent shape. I added a brush strainer and a drop T replacing the outlet baffle as the baffle had started to warp and I wanted to catch any large particulate keeping it out of the drain field with the strainer. After one year with the strainer in I dug up the lid to pull it and was amazed at the crap(no pun intended) it collected. Not wanting to destroy the yard every year I'm going to cast new lids with 8" plastic drain field tile installed in the lid during the pour and cast concrete caps to seal the tile at ground level. I know I can buy commercial risers, but I didn't like the idea of cutting large holes in my existing lids without knowing how much reinforcement they have and commercial riser/lids are pretty pricey. Does anybody have any thoughts or other suggestions regarding my plan?
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