Hmmm,
Perhaps the inventor hasn't heard of a loofah or a long handled shower brush.
Not wishing to rain on this inventive parade but................
Surely if an individual was unable to reach their feet, eg. because of disability .
Then how does Mr/Ms inventor anticipate the persons gonna carry a washin up bowl full of warm, soapy water about?
If they could ask someone else to assist with the carrying of aforementioned receptacle then wouldn't it be easier to ask the assistant to wash the feet to start with?
I too have a wonderful idea for an invention....
Person a). (Able bodied, pinny in situ).
Person b). {Recipient of service} Places left foot in washing up bowl of warm soapy water.
Swish foot about for 2 - 3 mins, place appendage in fluffy towel upon a)s knee.
Repeat process with other appendage if available.
TADA

... Nobody copy my idea though, as patent is pending.