I was hoping some one would mention these, I remember them a lot but I'm old and have no idea if they're still legal much less in use .
I once had a tiny house in PO-mona, Ca. that had been built as the sales office for a post WWII housing tract then when all the lots were sold they kinda - sorta added on a dog legged kitchen and sold it as a two bedroom home....(it was cheap & nasty but I only paid $49K for it) .
It was _slightly_ lower than the sidewalk so drainage was often a problem, after I gave up living in it and rented it out my best tenants 4 year old son discovered an abandoned dry well behind the house when he fell into it ~
Luckily he wasn't hurt and the tenant drove a Ready Mix Concrete truck so he just filled it in with some left over materiel .