BiggerPockets

I was looking into your problem, and found an interesting answer. Basically, you are responsible for any damage caused by tree roots, bad pipes, or other natural wear & tear. If the clog was caused by your tenant (by shoving something down the drain that didn't belong, or otherwise), they should pay. You plumber can normally tell you what the cause was.

I'd consult your RE Attorney to be certain, though. Also, check your rent agreement to see if you've got anything included in it.

If property is a SFR, then tenant should pay unless it is roots, etc. The best solution is to make ANY clog after the first 5 days of the lease to be the tenants' responsibility.

In a multi-family, it is harder to pinpoint who is responsible so offering to split that cost might be appropriate.