Yes, the "C" clamp does work. I have cleaned them like that for years & long before they started mas producing them.
I start with a breech fouling scraper & I scrape the breech, tip the rifle muzzle down & bump it with my hand to jiggle the loose fouling out.
Then put a gallon of Cold water in the jug & a squirt of dishwater detergent, then the hose from the C clamp in the jug thru a small hole drilled in the jug lig. (If you don't you will find out why)
Then you lay the gun upside down in a cleaning cradle (Walmart) & remove the lock. Clamp the lil C clamp over the vent. (If you have a removable vent you can now remove it if you wish & screw in a fitting with a tube & it connects to a jug same way)
Take your cleaning rod with a Bore Guide & a appropriate jag & a good thick patch, wet it & push it down the bore. When you pull it back it will suck the solution into the bore. Swab back & forth 10-15 times. Change patches, do it again. 3 patches worth usually does it. At that point when you have the barrel full, stop leaving the barrel full & most of the rod hanging out of the rifle & let the breech soak. Now go to the faucet & take a toothbrush & clean the lock. Dry the lock with a paper towel. Completely saturate the lock with Ballistol & set asside to drain.
Go back to the gun & pull out the rod, tip the gun up & drain the fluid into the jug. Put on a breech brush & brush the breech just to be sure. If any residue, reswab as before. Usually there is none.
Now take remove clamp & lay the rifle back into cradle & put a rag over the vent. Put dry patches on the jag & swab with several, changing patches til they come out dry. Now wad 2 of them up & stick them in the bore & take a jag & push them tightly into the breech & hold for a minute to absorbe any moisture your jab patch may have missed.
Take out the rod & put on a worm & grab the 2 patches. Squirt some Ballistol down the barrel & into the vent, wet a jag liberally with it & swab the barrel, WITH a rag over the vent or you will oil the wall or someone. Swab barrel real good & quit. Install vent if you had it out, wipe down the lock & install it. Put the gun away with the muzzle down. Reswab 2nd day. Reswab 3 day.
It takes me about 15 minutes to completely clean a longrifle or a halfstock in this manner.
I don't use hot water as it makes the barrel flash rust. IMHO. Think not ? Polish a piece of steel & put it in hot soapy water & clean it real good, pour boiling water over it & then immediately put it under a microscope & see what forms. If you are cleaning your gun & using hot water & stop after the boiling water part & talk for 5 minutes, you barrel has already flash rusted while you were a yappin.. I never us peroxide in any cleaner or lube. Same way if you swab with alcohol, you better be a shooting it or oiling it as you just took all the rust inhibitor off the bore.
There are no doubt hundreds of successful ways to clean a ML successfully. But to me the Most Important thing to remember is to get the Moisture Out. You can still have cruds in it & if you use a good preservative it will most likely neutralize it.. But if you leave moisture in there, it WILL rust.