Extreme cases require extreme measures. I've washed extremely dirty electronics successfully in tubs of water too. I note he removed the CMOS battery. A good thing. He also didn't use water on the power supply, or fans.
Oddly, when washing, it looks like the CPU is still mounted to the board. Yet around the 8 minute mark, he's mounting the CPU, so not sure what really happened. Regardless, I would have removed the CPU for the washing part. Not all IHS (integrated heat shields) are completely sealed. Plus, with the CPU removed, you can clean the socket.
I also take my electronics outside to blast out the dust with my air compressor. I never clean out dusty electronics indoors. My nose would never forgive me. Plus, why toss all that back into the air where nearby computers will pull it in again?
I would also use my air compressor to blast out any and all remaining water from the sockets and cracks and cervices after the last rinse. Then, just to be sure, I would leave the board in a warm dry place for 24 hours before re-assembling.
If you don't leave the circuit boards submerged where water can seep and soak in, this should be no problem with modern electronics. In the olden days, they used paper wound transformers, coils and capacitors. You would never want them to get wet. But they are not used anymore. And unless damaged, the epoxy resins used to seal the edges of multilayered PCBs block water from seeping in too.
That was certainly a filthy computer. I've seen considerably worse. Dawn dishwashing soap (what they use to wash spilled crude oil off water fowl and other wildlife) with a soft paint brush works great. And for the record, oily cat hair and dander mixed with tobacco smoke and years of dust accumulation is, by far, the worst. You almost need a hammer and chisel, or at least a good putty knife to get it off. Doesn't help I'm allergic to cats.
Also, I highly recommend the use of a properly equipped air compressor instead of cans of dusting gas. Note I said "dusting gas" and not "canned air". Those cans of "dusting gas" do NOT contain “air” and therefore should never be called “canned air”. Instead of safe-to-breath air, they contain difluoroethane or a similar gas. These gases are typically used as refrigerants and can be extremely hazardous if inhaled. In extreme cases, it can damage the central nervous system, or even be fatal. So use in a well ventilated area or better yet, outside. Note in some jurisdictions, these are controlled substances and sold in a controlled manner, similar to how cans of spray paint are sold to [hopefully] dissuade abuse from “huffing”.
Last, whenever using an air compressor, ALWAYS - as in EVERY SINGLE TIME - use a inline moisture and particulate filter to clean electronics (or air-brush painting birthday cakes and faces). The compressing process WILL create condensation inside the tank. This condensation collects on the walls of the tank, then runs down to the bottom. Nasty, rusty water particles and other contaminants pulled into the tank can be spewed back out and onto your electronics - never good.
