Booster pump to increase pressure:

The drain in your RO system is fixed by the flow restrictor, the drain will be the same regardless of input pressure.
If you want to have less waste water coming out, then you just need to change to a smaller flow restrictor in the drain line of the RO system. We do offer smaller flow restrictor if you want to purchase, which is $8
If you have an external type flow restrictor, then there is usually a number written on the device, this number is the drain rate, if it says 500 then it means 500 mL per minute.
The booster pump you purchased is to increase the input pressure to the RO system and increase the production rate, so that overall production rate vs. drain rate will be better thus, more efficient.

Booster pump 6800 series is for RO system that produces 18 up to 100 gallons per day.
If RO system is 100 GPD to 150GPD then you can use 8800 pump.
If RO system is 150 to 250 GPD then you use 8855 pump.