Updating the knob and tube might just be flushing cash down the sink unless you can get a solid return on all of the upgrades. 

Sometimes towns flush water hydrants or do work on main water lines.

The plumber told me that it is clogged with grease from my tenants kitchen sink drain and he recommends that we get it hydro flushed. 

The panel is supposedto be flush with the wall surface.

I don't know if gnats are a symptom of anything in the house except leaving the screens open or drains needing to be flushed (vinegar/ammonia).

Running water, electricity, heat, flush toilets?

This antisemitism, more than anything, is what's driving these lies that all landlords are super fat, greedy misers flush with cash and therefore, it's okay to strip landlords of their rights.

I had a similar situation with property damage, one of my tenants flushed a medicine bottle down one of their toilets and backed up the whole plumbing system. 

The cause seems to be from the tenants flushing condoms, wipes, tampons, etc...

Once in a while I’ll also fill the kitchen sink full with hot water and then pull the drain stopper to let it flush through.