When it starts cascading onto the floor, it's only a matter of time. Sometimes it's a slow trickle; other times it pours. Gradually it forms pools and puddles. Then it's wall to wall. Then the level rises, sometimes to the ceiling. It's not water; it's clutter. Clutter gets backed up and starts filling the house when it flows in faster than it flows out. Draining the house is what we do when we finally realize we're in too deep.
In the normal state of affairs, stuff comes in and stuff goes out. Buy a bunch of bananas, eat them, and compost the peels. Buy a bag of new socks, wear them until they're threadbare, and throw them out. One in, one out. If stuff goes out at the same rate that it comes in, then there's never any buildup. The only need to drain the house is the periodic carrying out of garbage and recycling and donations to charity.
The outflow is faster than the inflow under certain conditions. Moving away. Hopefully the truck is getting loaded faster than anyone is carrying in new shopping bags! Having a yard sale, many of the contents of which may originally have come from someone else's yard sale. Declaring laundry bankruptcy and spending an afternoon at the laundromat. Major space clearing, when we realize that the house needs to be fully drained.
Usually, stuff flows into a house at a faster rate than it flows out. This is the nature of the vast material wealth of our society. Paper that would have been precious to the ancients is foisted upon us in endless drifts of junk mail and coupon circulars. Entire stores specialize in selling goods for one dollar. Others sell recycled/donated items they collected for free. Others are known for handing out free samples. Things are so upside down in our time that poor people can wind up having more stuff in their houses than wealthy people do.
What I tend to find in my work is:
Laundry carpet - so many clothes that they are strewn across the floor, and the flooring itself is invisible. Carpet? Tile? Hardwood? Who knows?
"Why is there a pot on the floor?" - so many dirty dishes piled in the sink and on the counter that there isn't enough room, so some have to go elsewhere. On the floor? On the dining table? In the oven?
Mail blizzard - so many papers that they cover every flat surface, sometimes to be moved into bags and boxes so the surfaces can be covered again, like bailing out a boat
Cupboard explosion - so many plastic food storage containers/coffee mugs that the cupboards are too full even when the majority of items are waiting to be washed. So many food packages that cases of food are stacked on the floor for lack of storage space.
Bags in a box in a stack on a pile - so many items of every description that they can't even be stacked anymore. This is when the level starts to climb past three feet or higher.
No free space, either vertical or horizontal - everything flat has a pile on it, unless it's vertical, in which case it's covered by a bookcase or a stack of bins or a bunch of refrigerator magnets. Not so much as a single square foot of blank space to rest the eyes.
The worse it gets, the worse it gets. The deeper the accumulation of dirty dishes, the more dishes are "needed" so that there will still be a clean one, somewhere. The wider the stream of dirty clothes on the path toward the washing machine, the more clothes are "needed" so there will be something somewhat clean to wear, somewhere. The more papers there are, the more magazines with articles on Getting Organized are "needed" to add to the stack. The less comfortable it is to live amongst the rising floodwaters of clutter, the stronger the need to be out somewhere, away from it all, which usually means a manufactured need for a shopping trip. Every trip outward, escaping the mess, tends to result in at least one shopping bag that comes in. Nothing is going out. The floodwaters continue to rise.
A house won't drain itself. Usually it is only initiated by unfortunate external events, like an eviction or a natural disaster. Once I saw a photo some acquaintances had posted of their kitchen after a major earthquake. Quite honestly, it took me a minute to realize that anything had happened, because it looked like any other messy kitchen with greasy cobwebs. "This place looks like a tornado hit it." Mean, but sometimes true. When the piles of clutter get too high and too deep, it becomes impossible to tell if real disaster is going on underneath, whether that's a hidden water leak, toxic black mold, or an infestation of vermin. Then the clutter becomes the least of the problems.
Draining the house voluntarily is a very brave decision. It's hard work. The accumulation of years won't disappear overnight. Usually it starts to look worse for a while even after a lot of strenuous work has been done, exactly like rebuilding after a flood. The detritus has to be cleared away. Usually it reveals stained carpet and damaged flooring, marks on the walls, and damage to various fixtures. Years of deferred maintenance start to reveal themselves. That's why we remind ourselves that we don't have to do it alone. Rebuilding is done in groups. Drain the floodwaters, and ask for help so you don't get in over your head.
I've been working with chronic disorganization, squalor, and hoarding for over 20 years. I'm also a marathon runner who was diagnosed with fibromyalgia and thyroid disease 17 years ago.