It is not just about stains it is also about vacuuming and if you don't vacuum every little thing shows on a dark carpet.

Once the carpets are a little dryer, pour a crap load of Glade carpet deodorizer and then vacuum it.

Also shop vacs are amazing over your normal vacuum for jobs like these.

Treat it like you would your own house if managing yourself yearly inspection :- furnace/boiler - clean out burners (do in Fall to make sure heat is on in winter)- clean dryer vents- caulk bathtubs- change out thermostat/CO2 detector batteries- clean out gutters in Fall- while on the roof looking at gutters, take a look at roof condition - fix early- vacuum and clean utility room near any furnaces and water heaters (keeps dirt/dust out of systems, can extend life)- rinse water heater screens (can fill with dust and won't stay lit)- drain water heaters yearly - prevents sediment buildup and will extend life- change furnace filters (more often than yearly)- if in cold environment, turn water supply to exterior off before winter- take a look under sinks to check for any slow leakThis shouldn't take much longer than an hour or so per unit per year unless you find something unexpected, and if you do find something then good job catching it early. 

I vacuumed and used compressed air to clean and they been fine since. 

.- The tax advantages cannot be considered in a vacuum, but only in conjunction with everything else.

First, my W2 job is being a Logistics Analysts for the largest manufacturer of vacuums/carpet cleaning products in the world.

While the seal might not be air tight, it may be causing a slight "vacuum" due to reduced venting when flushing the toilet, emptying a sink or draining a tub that pulls enough water out of a trap to allow it to backvent up through the trap.Is there another sink, laundry, dishwasher, etc. that was added at some time in the homes life in a spot not originally constructed?

So, usually I just have to vacuum the carpet in their room and clean their bathroom.

Tenants eating on the carpet and not vacuuming right away.