The salty sea water could even become the water to flush your toilet with as one use for the waste?!
I agree with the above, the scale of the proposed system shouldn't lead to sealife issues.
I don't think running saltwater through a toilet is straightforward. You would need higher quality parts, more frequent valve maintenance, and downstream waste processing equipped to handle the salt.
Sailboats use sea water in their toilets all the time but using it would require two systems, one fresh and another brackish. Very doable but more expensive. I believe they've also use grey water for toilets and plants but again it requires splitting the systems and having storage.
