There's a float that stops any additional RO from going into my storage tank which is then supposed to build up enough back pressure in the unit that it trips an auto-shutoff valve to stop the water from coming in to the unit. My pressure is too high and the auto-shuttoff doesn't work so the RO unit continues to run. BRS even sent me a replacement in case it was bad, but it wasn't the unit...it was my house. I hooked my RO up to my fridge's water supply line just for sh*ts and giggles and it worked fine.
Since there is a float valve on the product (RO) line it doesn't actually fill the drum any more or cause a flood, but it does run out of the waste water line until I shut it off by hand. Burning out my carbon and sediment blocks.
It's all my fault....I have EXTREMELY high pressure and made the mistake of tapping for the RO unit before the home's pressure reducer instead of after it. And pressure greatly affects an RO because the more pressure, the faster it produces. If you have low pressure your 75GPD unit may only produce 40 or 50 GPD..that happened to my on my LAST house with a well. So this time I said...I'LL SHOW YOU...and tapped right were the water enters the basement to get the most pressure I could from the city. [hand slaps head] Oh well.
Anyway. I have a float in my drum to stop the RO and a float to my sump to control top-off so technically my RO has a direct line to my tank...a very dangerous thing if you don't have checks in place. In my case the check was SUPPOSE to be an electronic system that only allowed the water to feed the RO a few hours every few days but the solenoids I bought couldn't handle the d*mn pressure either. So for now I just turn the feed line on once every week or so (depending on how fast I deplete the top-off) by hand. So for that stretch of time my RO is on it won't flood anything because of the floats, but if I should have a leak or a sump pump go ape-sh*t and spray water out of my sump, the top-off will try to replace it and then the RO will CONTINUE to replace it and plummet my salinity.
I tried to make the system as autonomous as I could. Once I get the new water timer in place and stable (it's built, just not running yet) my tank could go for months without me needing to touch it. All I need to do is clean the skimmer once in a while and do my W/C which is done with pumps and switches. This is all in the basement out of sight and out of mind. Of course I have to feed the fish and I'm constantly battling coraline on my acrylic, but I've built a pretty hands-off system in terms of daily crap.