You have 2 options to go about it, and you know the tenants and will know what they will react to best. 1) Offensive-- prove with a plumber they are causing the issue, and they are responsible and per the lease, must pay for the plumbing damages.   

Please don't take offense, and I genuinely hope that it works out for you.

The discharge for the pump would either  go to the main waste line or exit outside somewhere.please do not take offense by this but you should really  try to learn the basics of how a home is constructed and what makes them function.

No offense but that could be a $7-10K mistake if you didn't see it and think a seller will replace it.

I never want to insult a QUALIFIED or unqualified applicant I am upfront about what I’m looking for I usually state the following VERBALLY to people before they apply - Your credit doesn’t have to be good to apply, you will still be considered - I just don’t want violent criminal offenses, but if you do have one, please explain - I will be accepting up to 15 applicants for this home, the most qualified will be accepted - DO YOU have anything else to add?

If the tenant is in breach during the initial term, then you would need to issue the appropriate notice to cure whatever the offense is.

(no offense meant).

I think first offense is a 20k fine. 

Tell them this is the final warning and another offense will result in termination.

And, no offense, really.