Tried to get fixed, sent videos even let the maintenance use my hose/water to see where the issue is. 2017, maintenance came and caulked outside of building (these are stacked condos and I am on the bottom) after doing same tests 5 yrs earlier.

This is used to store gardening tools used for yard maintenance and other miscellaneous items; hoses that I remove from faucets and store away during the winter, my left over bag of concrete for those quick DIY jobs, ladders, etc. 

Your opening yourself up to getting completely hosed if your not following regulations.

Try snaking the vent pipe and pouring hot water down it or sticking a garden hose in it.

The washer wouldn't stop filling up, it turns out there is a little fishtube hose back there behind the timer that sometimes pops off.

It's a little bit of a pain but you could pull the dryer out, disconnect the vent tube and run a vacuum hose through it.

How many owners check the hoses to their washing machines, ice makers, refrigerators, under their sinks, etc. on a very consistent basis (if much at all)? 

Depending on the type of roof and your ability to overcome your vertigo, you might take a hose up on the roof and have someone in the attic watch for drips.

exterior garden hose bibs need to be covered etc.  

Often it is a flex hose which can cause problems with lint build up.