Actually, I had the same problem with the water flow, you have to do a little bit of extra work.
First, you do need to unscrew the water connection to the toilet. In addition, there is a small valve there that you will need to actually remove (I think it is a single screw that holds it). Once you get that out, you will probably find there is some leftover calcium in there that is blocking things. I also ran a piece of large fishing leader -- think .090 gauge like for a weed eater, in through the outlet side in the toilet until it came out where the valve is.
Since you have already cleared your lines, once you do this, you "may" be good.
You will want to check your pressure/flow with the hose removed just to make sure it is flowing, then put everything back together.
I know you said it is at the shop, but this is what I had to do -- 2x's.
What I believe happens, and filters aren't going to help here, is the calcium in the water solidifies when the water sits in the lines for a period of time. This seems to be especially true if the RV sits long enough to where there is some evaporation that can occur within the lines. This is what I had coming out of my valve and hose when I unclogged it -- and yes, I do have filters as well.
As a side note, unscrew the bathroom faucet screen piece, this accumulates the calcium as well and will restrict flow there too.
2013 Georgetown 351
Much more significant other....
2 Kids and a dog that rules!