Another septic tank riser issue

It must me something in the air. At least it is when you pop the lid -LOL! Anyway, I asked that the backhoe operator allow for a cleanout for the septic tank (long story - not new construction) so he left two, 6" PVC pipes with covers on them. Something posessed me to look inside them after three years and the 6" pipe is apparently a shield around a 4" line that goes to the tank. You can look right in on the discharge end and all I can see is more PVC at the bottom of the intake side. Funny thing is that I only see a little bit of water trickling through on the intake side when I flush - no solid or paper. Well, it's coming 'round to mandatory clean out time and there's no way that those pipes are going to allow for a pumping truck's hose to do a good job. I need to put in some risers and a lid, down the 23" to the tank. Which end? Or do I do both ends of the tank? TIA, Chuck
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