Do you think this water saving mod worthwhile?

path1 wrote:
Does anybody see any other downsides to this mod?

A simple valve separating the waste and fresh water is not going to pass safety code.

You need to be full time with one or the other. Or you need a real backflow device not one of those $10 jobs.

No I would not do it. At most I might capture the sink water in a bin and send it to the black tank to save space in the grey tank.

I am far more likely to add more tanks if the space was that important.