First, when dry camping the fridge and water heater controls, furnace, water pump, lights are powered by the battery. Did you check it for water, voltage before andafter charging? A 12v battery should last 2-3 days on lite usage. Furnace is the killer.
Water smell and taste should not be your issue to flush. I assume you have a good sanitary well.
Rental units water should be sanitized every time they come in. In my state a complaint to the dept. of health will send an inspector to the business. Assuming the business is on a city water system, they are not required to test and sample their potable water, but who knows where a previous renter filled it? Or how long it sat unused.
Get your AHJs (auth. having juris. ) involved on health and safety. It could identify more than lax policy in the rental co. but also a bad water problem a previous renter used. You may save many people illness, poor reviews to the rental co., and have them begging to refund your fee.
I manage an EPA transient community water system. Water potability is our highest health concern. Private wells and community wells that serve less than 25 persons, are not regulated or required to test for contamination.
A foul odor after flushing is likely H2S, hydrogen sulfide, caused by total coliform or even fecal the dreaded e- coli, bio film build up which accumulates and is resistant to chlorine sanitation up to 10 mg/ L when left unused during sanitation cycles.
Continuous chlorination is only effective when the source is proven safe, contact time in a holding vessel is sufficient, otherwise the same as in a swimming pool the bacteria can overwhelm the sanitizer, resulting in bacterial growth which can only be sanitized by 'Shocking ' with a high dose of sanitizer for an extended period of time, depending on the dosage. I.E, 50 ppm for 4 hrs, 100 ppm for 2hrs etc.