Plumbing/sewer question on a fourplex regarding ejector pump/pit.

[Navid A.]

Hi

I bought a fourplex a month ago. Two weeks in, I had a complaint of raw sewage in the garage of one of the units. They did snake the pipe and baby wipes came out.  The problem solved for the time.

A few days later, another unit started having sewage in the garage. Plumber mentioned there is a ejector/grinder pump in one of the units that handles all sewage from all 4 units.

They replaced the ejector pump and in 2 weeks, same issue happened with the sewage leaking in the garage. The plumber came back saying the either the pump was burned/failed because of too many wipes being flushed down or when "an outside vendor" did snaking the pipe, it damaged the pump.

He also mentions the "pit" where all the sewage from the fourplex comes to is too large, corroded and needs to be fixed:

"using gravel to fill in the existing voids present around
the pit, then install a new pit with the extension lid
needed. Once the new pit is installed we’d install a
proper vent to restrict the sewer gases from getting into
the home. We’d complete repairs by re-concreting
around the lid of the pit in that garage floor. Estimate of
$5,250 to complete this."

My question is, is that really necessary to "upgrade" the pit? My concern is that I do not want to keep replacing the "ejector pump". Not sure why the ejector pump failed after two weeks. 

I had the property manager to issue notice to tenants to stop flushing down baby wipes! Below is a pic of the "pit" which the plumber says its too large.

Any feedback is appreciated!

Thank you.