Need to seal off my main drain at the bottom of the pool

[Frank-pool]

I have a 40 year old pool in Brevard County, Florida. Over the past couple of years I have had several leaks in the main drain pot at the bottom of the pool. I've had American Leak Detectors (ADL) come, identify the leaks and use epoxy to seal them. The leaks are coming from cracks in the plastic of the main drain pot, near the top where the several resurfacings I've done over the years have no doubt stressed the wall enough to cause the cracks. This latest leaks however has been so severe that ADL has advised me to seek a better solution.

Please note that this "main drain" is NOT where the water is taken to the pump system, that comes from my skimmer box. That main drain pot is six inches in diameter and seven inches deep. There is a plug at the bottom which at some point was pretty much buried in epoxy; that plug has never been removed to my knowledge. There is also a port on the side of the pot, the line from that leads up to the skimmer box. The line is intact (ADL tested it) but I've never, ever used it to drain the pool, nor has the companies who have done the resurfacing. And over the years it is so blocked with debris that when I drained the pool, well, the pool really pretty much drained itself, no water flowed at all from the skimmer box down to the pot six feet lower.

So I want to just seal off the entire main drain pot. The pool is completely drained and dry. My instinct is to get some hydraulic cement and fill the hole, but I'm concerned that since the main drain pot is plastic (PVC?) that the cement will not provide a complete seal and will allow water to seek around it to the cracks in the pot. I've considered trying to get a professional pool repair service to come do the fix, but the only one I've called so far seems to know less about pools than I do. Even if I do get professional help I'd like to have some information from you folks so I can figure out if the professional knows what they are doing or just blowing smoke.

Thanks for any help folks here can give!