Even two months of not using it shouldnt have had that much build up in it, it takes a while for that to build up on city water.
what else is supplied off that water line? they connect somewhere in your house, find the closest faucet, turn the water off at the main coming into your house, and backflush your lines, just open the one closest to that spiggot you used to hook your unit up to.
Ive done ALOT of plumbing work with my grandfather and even the cabin with city water we didnt use for over two years didnt have any build up in it.
what color is the water coming out of that supply line? I think your unit is messed up not your line, every time you use water in your house it pressurizes the lines and always has fresh water in it. Im just saying two months will not cause a build up like that, even with well water( unless its a very rusty well then you got more issues then worrying about a RO
I had a 3 filter RO
unit for about 10 years in my house, I recently ripped it out and threw it away(mainly due to being outdated and filters and resin were really hard to find for this unit) I just buy spring water now for 39c a gallon, fish seem to respond to this water better.
The only pipes I know to turn sediment orange is iron, copper turns green and brass does as well( I think brass does, I havnt seen that used on residential plumbing in a long time.