Hi, I’m a mobile hairdresser who specialises in hair for older and disabled clients so this was something I had to figure out at first too
I use this mobile backwash
https://www.ebay.co.uk/itm/22359612...=2047675&ssuid=&widget_ver=artemis&media=COPY
Honestly - it was the best investment I ever made. Because it is height adjustable and portable you can literally put it right up to their neck even in a wheelchair [or a normal chair works as well, it’s sturdy so they can lean their weight back on it]. It has a waste hose which I just put going into a bucket underneath to catch the waste water, and I use a usb chargeable camping shower pulling water from another bucket [but that is because I work in people’s homes, so being able to wash in a living room is a must - you probably could pop it next to your backwash and pull the tap over]. You can get smaller depth basins but personally I prefer having the deeper one as less chance of spilling or splashing. It fits in my car so I can take it wherever. My clients absolutely LOVE it - I can literally do their whole appointment from one chair if needed without them needing to move, so for someone housebound or wheelchair-bound it was perfect.