Here is what I did to save a lot of water. I wanted to move away from flushing 200ml of urine away with 5>9 liters of pot able water. It started by me standing over a bucket while showering, then 2 buckets with a foot in every bucket, then me standing in a oval plastic wash basin. I then use the shower water to flush the toilet. I then got tired of carrying buckets around. I decided to dig a hole and plant a 200 liter blue plastic drum to catch the shower water (to prevent a possible collapse of the tank by the soil I filled the area around it with coarse sand mixed with dry cement, it became hard by drawing moisture from the surrounding soil). From the drum I use a small pump to transfer the water to a other container (68 L Rough Tote box) on a stand 1m above the toilet cistern. From there it is connected to the toilet cistern through a Stockman float valve (high flow low pressure valve).

I use a normal float valve to control the level in the top box. I manually start the pump to fill the top box but I have a timer on the motor to stop it after 2 min or longer. If the need arrives I can still open the municipal water supply to the cistern if there is not enough showering vs using the toilet going on.

What I found so far: never use washing machine water in this system as it starts to stink in 24hrs, normal untreated graywater takes about 5 days to become noticeable. I pop a chlorine pill in the underground tank (it last about 45 days) and if you flush the toilet there is a faint smell of chlorine which smells clean and fresh. I put a piece of shade cloth bag over the UG tank inlet to catch hair before it enters. There is a fine mesh filter between the UG tank and the top box, but it is of very little use after installing the shade cloth filter over the supply pipe.

With a low flow shower rose we generate a little bit more shower water, than the toilet uses except if we get "non showering" visitors but this happened only once. If I see the UG drum have a bit too much residual water, around every 3 days, I change the pump outlet to the hosepipe and then water the garden.

Previously I had to clean the UG and top box every 2 weeks due to funky smells but after not using washing machine water, the inlet filter and the chlorine pill everything is still smelling fresh and clean, the wife will inform me very fast if something starts to smell off.

We have nearly halved our municipal water consumption and now my garden gets more water than it ever did before.

The pump can easily be moved to another blue 200L drum which collects the washing machine water but that gets pumped to the garden asap.

Total diy cost was about R1000 (R400 second hand 0.37kw pump, R250 Stockman valve, R160 Rough Tote 68 liter box, R100 float valve for top box and then some pipes and gardena fittings and scrap wood and iron to build the stand).

Enjoy, it can be done.