Advice Needed: Install Tank Riser On Old-Style Tank Top

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New Member
Mar 26, 2021
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North Carolina
My septic tank was built in the mid-1960s, and it is what folks here in NC call a "homemade tank". The tank walls are made of cinder blocks and it has four 4.5' X 2' X 3" thick concrete slabs laid across the top of it, one of which must be "flipped-over" to pump the tank. The top is about 12" below the surface of the yard.

Needless to say, it is a hassle to excavate it every five years for cleaning. I would like to install a 6" clean-out riser on topo it, but I am terrified to try to create that big a hole in one of the old, deteriorating 3" concrete slabs. Is there anything with which I can replace one slab that is sufficiently "workable" that I can make a 6"+ hole in it without compromising its strength? I had considered fiberglass decking material, but it would be very expensive, even to replace just one slab. Any ideas? The system is working as it should and I can't afford to replace the whole tank (and probably the field as well, due to "codes") just to address this problem.