Their landlord wasn't very friendly, and would not occasionally surprise them with a gift of booze and porn mags.What are the mistakes you've seen other people make?

A simple clean out of the drain tube and problem solved.

Being as the audience seems to be college students I'm sure referring them to DIY you tube videos on basic household maintenance would be a hit.

Just be careful, you don't want to find out half way through the job that he didn't know what he walk taking about.Watch out for lead pipes, leaking main lines, plumbing that goes from galvanized, to cooper, to pex, knob and tube wiring...etc...These things will turn your investment upside down. 

Hello,I had a tenant last winter and the heat in his unit was supplemented by the unit above him.It gets really cold down there in winter but he chose not to have free heat and sealed the vents tightly with an aluminum foil without  letting me know , I could have easily adjusted the thermostat to lower  per his needs if he had told me and supplemented my apartment above with any additional heat but he chose to seal without letting me know inspite of my warning later on and obviously it can have detrimental effect on the tubing inside the walls due to excess pressure build up.He also complained about high electricity Bill's (obviously he would incur high utility bills when he turns on his electric radiator without using the free heat he was getting) I ended up having an oversight from my end as I did not verify if sealing vent caused any damage . 

Galvanazed steel pipes and potentially even knob and tube wires (rare).

I've learned simply by watching U Tube, here on BP and hands on experience.

Otherwise, at no cost to you is You tube University.

Very simple to do,  watch a you tube if you are not familiar or hire a handyman if you are not comfortable with electric. 

@Taylor SmithBe on the lookout for powder post beetles, knob and tube wiring, lead based paint, and deteriorating fieldstone foundations.