Must all be level and flush.

If the apartment toilets continue to flush OK, the sewer line may actually be clear and fine.

How specific can you get in your lease when it comes to tenants responsibility for repairs of things to the house related to negligence, ie flushing sanitary products down toilets, appliances, hoa fines related to negligence of caring for the yard or following hoa rules etc? 

Everything Paige said and a few more.All vehicles must be licensed, tabbed and operableNo water beds, pools, portable heaters, portable dishwashers, portable clothes washers or dryers shall be used on the premises without prior written consent of agent/owner.No dust, sand, dirt, rubbish, coffee grounds, feminine products or other foreign material shall be flushed or washed down toilets,sinks, or wash basins.

I also let the tenants know and not to pour bleach down the drain or flush hygiene products (which they shouldn't flush anyhow).

Tub/ shower,  kitchen.Let them run for 5 minutesThen flush all toilets with some toilet paper in it.If toilets take more than 5-6 seconds to flush down then you have a problem. 

That seems like a much better deal than “flushing” $100k plus of your $300k-$400k expansion money there’s almost no chance you get back.

Remove food that can rot, empty the trash, flush the toilet, etc.

From a purely water reduction perspective, a low-flow, dual flush (0.8/1.28 gallon) or single flush 1.28 gallon toilet if you don't think your tenants can master the dual, will save you the most ... especially if you are removing old 5-gallon/flush toilets.

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