If you want to stick to the DC/MD/VA area, you might want to consider house hacking a SFH and Airbnbing an extra level/room/basement/crawlspace/fallout shelter-- like you said multis are few and far between here, but you might be able to find some in areas that show up as that beautiful deep navy blue on the Trulia crime map.I live in northern VA but do all my investing outside the area. 

This show will go down in BP history as one of the foundational episodes: Brandon Turner and David Greene dive deep into seven unique and powerful strategies for building a real estate business that can fill your life with cash—not work.

Being this deep in the hole is an incredibly serious situation and the message that gets delivered should match that seriousness in tone. 

Deep down I want them out, but I think it also terrifies me to have the place vacant.

Its not easy being an agent or investor so you don't want to jump off the deep end and fail at booth.Also if you find this helpful please don't forget to vote it up

On the other hand, it it was buried 8’ deep, or 50’ away from the house, etc. that is a better reason they didn’t find it.

Groundwater is usually not impacted as you will not know since most tanks are only 4-5 feet deep and you will not encounter groundwater in the tank pit. 

You could lose this thing as Jay mentions... this was far more common coming out of the deep dark recession.. but now a days builders don't need to do this and if they need to do this means they are either long on jobs or short on capital.   

What you have suggested in the OP sounds good, but rest assured if there is an incident, the victim will sue the "deep pockets" landlord before the "blood from a stone" tenant. 

I invest solely in deep East Oakland.