I use one of those Walmart special pressure reducers... I think it is actually by "Campmor"?
It does reduce direct water pressure coming out of the faucet, but the water volume is decent. Noticeably less, but usable.
"Cutting down water going into the waste tanks" is all about how you use water, adding a pressure regulator / reducer really won't change that all that much. If you want to experiment, just add a simple on/off thumb valve to your water hose and put it to 1/4 or 1/2 open.