Guess What This Is ?

I'm looking to demolish a property and discovered these three vents/holes behind the garage. I know there is a sewer line near the one without a cover. The other two with the metal tops I have no idea about.

The block is 60's - was probably used as a milk bar / store of some sort and hasn't been used in many years. There is an alley about 6-7 metres behind it and its a corner block... so I'm wondering if there is a septic tank or gas tank? Water company doesn't have any tanks listed and they say nothing was done to the sewer since the 70's (which doesnt add up because of that plastic pipe).

What would you do next?
Get a shovel, dig it up and see?
Call a tank removal company to come out with a ground radar/scanner?

IMG_3857.jpgIMG_3854.jpgIMG_3852.jpgIMG_3858.jpg

Thanks in advance for your help. Any advice is much appreciated.

:):2tsup:
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