If you want to use a piece of tubing to siphon cool water up out of a bucket into the barrel of a flintlock, then my advice is to do the following:
Find a strong rare earth magnet that has a hole in its center that is smaller than the pipe fitting required to fit the tubing that will be used. Drill & tap the hole in the magnet to fit the threads of the pipe fitting. Remove the flintlock from your rifle, and if necessary, grind the magnet to fit the barrel flat exposed by the lock. Find a suitable weight with a hole in it to fit on the end of the tubing that will rest in the bottom of the plastic 2.5 gallon bucket. Super glue the weight to the end of the tubing.
Now you have a tubing siphon cleaning arrangement that won't come off of the barrel no matter what. The hole in the magnet will stay centered over the touch hole until you remove the magnet. No fragile clamps to mess with.
Personally, I just twisted a round toothpick into the drilled touch hole, filled the barrel halfway with room temperature water, sealed the muzzle with my thumb, & shook the rifle up & down a dozen times. Dumped out the dirty water, and repeat several more times. After 4-5 shakes, the bore is pretty clean. Now just clean with patches the normal way, again with room temperature water. To get the touch hole clean I just let water drain out of the clean barrel through the touch hole. With a flat-faced breech plug there are no nooks and crannies to clean, other than the touch hole. The lock always took longer than the barrel.
And remember, contrary to popular opinion, hot/warm water is not necessary to clean real black powder fouling. Black powder is hygroscopic, which in plain English means it attracts water/moisture. Cool, or room temperature water is all that's needed.