ADS Pipe Seal Question

First, a rather long winded background. I have a customer with an 60" ADS corrugated pipe (in three sections) that runs under a narrow creek crossing. The heaviest load it sees are a few horses. Last year I was called out to work on a washout problem on the outlet side that also received quite a bit of runoff from the sides. I regraded and compacted the bank and installed geo with 20 or so tons of 8x12 rip rap anchored on the banks. The inlet side looked fine at the time and the customer didn't want to mess with it. That said, I set about 2 tons of rock on the banks on inlet side. We had major flooding this spring and the repair didn't budge, but now there's another problem.

When the owner had the original pipe installed, they poured a vertical concrete footing at the inlet that starts at the pipe invert and extends 18" below the surface. The runoff found it's way under the concrete and is entering back into the pipe at the first soil tight joint. Probably have the bell installed backwards. My plan is to grade/slope the entrance and install heavy pond liner material anchored with rip rap to stop the inlet leakage problem. I've done it before with no problems several years later.

So here's my question. While I'm there I'd like to seal the interior at the joints. I've used WR Meadows mastic and fiberglass tape on exterior joints before, but has anyone used a product on the interior that's worked? Keep in mind that the customer doesn't want to remove and re-bed the pipe.

ADS Pipe Seal Question