Yes, which soap is important. Information is available online but, depending upon where you live, may also be obtained from your local water agency.

I had an interesting experience doing the research.

It started with the local health department and ended up with the Sate health dept. No one I had spoken with had ever heard of grey water and I had to explain it. The final answer was that I was not allowed to do it.

The water company was about the same amount of help. A plumber mentioned that the Water Company doesn't want us to use of grey water because they need the return water to make the sewer system work.

This is interesting because I am taxed for return water (based on how much water I use). They even bill me for water that I use for my gardens that never leaves the land.

Look for products that do not contain sodium. E.g., Sodium lauryl sulfate.

The "low hanging fruit" of grey water is washing machine water. That is the easiest to exploit and the plumbing involved is relatively simple. It's best to have a valve so you have the option of sending the water to the sewer system if you need a load using chlorine bleach. There are laundry detergents recommended for grey water use.

You mentioned a tank: grey water should never be stored but run directly out to the landscape. Grey water that sits becomes black water. Systems that store grey water exist, but they use filters and UV light to treat the water so it does not become "black". It's best to apply it directly to the landscape, under a cover of mulch or into a swale covered with mulch.

Years ago, when I had a top load washing machine, then the 32 gallons per load would have been good to recycle. Right now I have a front loader that scarcely uses 3 gallons per load. It is the shower water that interests me. We love long luxurious showers.

I am fully aware of Grey Water converting to Black Water quickly. The use of a tank is a temporary storage and it will only regulate the flow to the gardens. My barrels collecting rain water from the roof act the same way. A hose connected to the bottom of the barrel feeds directly to the plants as soon as any water is being collected. Most of the time, they are empty.

The tank for grey water will provide a continuous flow until it is empty and will not store water for more than an hour after it has any.

Is sodium the major offender to my system? Anything else to be aware?