How to stop water seepage in an elevator pit?
...which is to say, you need a sump pump, because you will NEVER reliably stop it from the inside, and there's not likely to be any way you can gain access to the outside of the pit to waterproof it properly - and "properly" does indeed mean "from the outside." If you cannot waterproof from the outside, all you can do is pump it away, in any basement (other than hillside ones where sometimes you can just pipe it away, but that evidently would let the tide in more effectively for your situation.) 

You can TRY painting things on the walls and caulking cracks or filling them with hydraulic cement, but hydrostatic pressure usually wins and the leak returns.