How to deal with a slumlord neighbor?

[Sam Leon]

Have you ever had to deal with another landlord who is a slumlord?

I am in a small condo building and my unit A is adjacent to another unit B.  I rent out unit A and the other owner rents out unit B.  I maintain unit A regularly and have a long term happy tenant.  Unit B tenants come and go and the repeat stories I heard from them is their landlord "doesn't do anything".  OK many tenants would say the same and it's none of my business.

But unit A and B shares a common wall, where all the plumbing supplies and drains are.

So when something happens in that common wall, my tenant would call me and his tenant would call him.

One time the wall was wet, and I opened up the wall on my side and found a pin hole leak on his copper pipe.

Another time the wall was wet again, and I investigated and found a broken dishwasher drain hose on his end, and why would anyone run a DW drain hose into the common wall only to have it looped back into the sink cabinet 18" over?  and all kinds of kitchen waste crap was spilling into the common wall.

Several times the toilet won't flush, and it's in the main drain, I went to investigate and have it snaked from the common roof stack to clear the blockage.

Roach infestation issues (most likely caused by the broken DW drain hose spilling food waste into the wall) happened along that common wall, I went over and did pest control.

I can go on and on and on.

Whenever there is an issue, it's always up to me to handle, because he would ignore the issue, or simply tell his tenant he is "out of town at the moment."  I can't let the problem go unresolved because it would affect my tenant.

It got so bad that when there is a problem in unit B along or close to that common wall, that tenant would talk to my tenant (who may not even be experiencing the problem on his end yet) to call me to come out to investigate because "his landlord is hopeless".

Yet this is totally unfair to me.

Any thought on how to handle issues like this? Yes technically speaking a common wall issue in certain situations are HOA responsibility so you can say just let HOA handles it. But it is a 4 unit building with 4 owners, and we have always just operate by having the owners fix their issues then seek reimbursement from the HOA account so as to not having to go through too many steps to solve simple issues.