I'm going to use the LTA as a guide to remedy issues and cover my butt.

I hope that stops now as all the issues should have remediated and we should see the rents coming from next cycle. 

Any parcel of real property for which there shall be no other purchases will be struck off to the municipality in fee for the redemption at 18% and the municipality shall have the same remedies and rights as other purchasers, including the right to bar or foreclose the right of redemption.

- request seller to remedy any code violations?

We offered some remedies, which they refused. 

Also, make sure you have proper property damage insurance and mold remediation insurance, also a cheap add on.

So need a great plumber who can get it unclogged or get it pumped out (cannot pump it in yard) as well as a mold remediation contractor. 

https://www.ohiobar.org/forpublic/resources/lawfactspamphlets/pages/lawfactspamphlet-11.aspxObligation of landlord Maintain in good working condition all electrical, plumbing, sanitary, heating and air conditioning systems, and fixtures and appliances you have supplied.If you have notified your landlord, in writing, of problems at your rental property or of an insect or rodent infestation, the landlord should remedy the problems within a “reasonable” amount of time.

This would start with securing estimates for both removal of the and any possible remediation of the soil in which is was buried.  

I would recommend getting a disaster/remediation specialist in there as quickly as you can to put ALL of your tenants at ease.