Sealing new outlet on old tank

[Euston]

The outlet duffle on my concrete septic tank was cracked and I replaced it.
What's the best product to use to seal between the new baffle and the tank?
The tank was broken out around the old pipe, and there is a 2-3 inch gap in places around the pipe.
How should this be filled and sealed?
Thanks. Should have 3 or 4 more days, before tank fills up, to seal the pipe, and want to do it right.
Thanks

 

[Jimmy Cee]

I don't have any experience with your situation but I do not see why a slurry of cement would not hold the baffle in place, just packed into the crevice. Or possibly one of the expansion foams sold to keep air out of houses. Before using that I would try to contact the manufacturer to see if the toxic environment of a septic tank would adversely react with that product.

 

[FishScreener]

Nonshrink grout. Regular Portland cement will shrink as it cures.