I just did a quick "Google" on Muriatic Acid and it seems it's just another name for Hydrocloric Acid.
I'm buying it for 80 eurocents a liter at the grocery store here in Sicily and it's labeled: "Contiene: Tra 5-15% ACIDO CLORIDRICO." Don't know the "Tra 5" part, but I'd guess it's a 15% solution of hydrocloric acid.
And I do just pour it in full strength, although it certainly mixes a bit with the water in the toilet and hose and becomes somewhat more diluted.
I've also gotten it inexpensively in hardware stores where it's sold as "brick cleaner".
It, of course, is strong stuff with bad fumes to be used with caution - I'm reminded of the old ditty: "Johnny was a chemist's son, now Johnny is no more; what Johnny thought was H2O was H2SO4."
aboard "Sangaris" - Santorin #68