First of all I think both dolomite powder and bentonite clay are fine for soil. I don't think they are salts.
But more importantly, I don't think your
toothpaste will be a problem for your greywater, even if you use conventional toothpaste. It's such a tiny amount of the product. Think of how long it takes you to finish a container of it, and then think if your greywater system and soil can probably handle that much product in that much time.
My 20 years of
experience with greywater is extremely low tech. Our school in Ladakh, India, has greywater piped from the bathing block and from the kitchen block out to some
trees. We don't have a shortage of water, so it's all pretty well diluted, though we've got 50 to 100 people at any given time using it, so that's a LOT of washing products and kitchen washing waste. We don't try to control the products people use so we've got laundry detergent,
soap, toothpaste, and god knows what kind of gick our teenage residents use. We've been using this system for 20 years and the trees seem to love it. The willows and poplars are on the bathing-block water so they get mostly soap, laundry detergent and cosmetics. The fruit trees are all on the kitchen water outlet so they get a little soap and a lot of food bits and nutrients. We did lose an apricot right after winter years ago, that was on the bathing outlet, so I wonder if the willows and poplars are hardier in the face of soapy greywater. We try to regularly alternate the canals that are fed by the greywater, but some of the trees are right at the initial outlet and so are always getting greywater every day and night of the year, including an apricot, a pear, and several willows.
I think the key is if there's plenty of water, the soil can handle most of what you put on it. Especially if you make mulch basins full of
wood chips as recommended by
Art Ludwig, I think greywater is pretty unproblematic.
If you have to haul your water from far away and will be using tiny amounts of water very efficiently, then maybe it would be concentrated
enough to be an issue, but then you could dig a small soak pit for that concentrated water. Also you might find yourself using smaller amounts of all cleaning products, in the interests of using less water to rinse. Oh, or you try start using
local sticks that you chew the end of, and you might well find that those make your teeth more squeaky clean than a reusable toothbrush with any kind of product.
I believe greywater is much simpler than you fear it is.
