I didn't have a specific use case in mind for this. I would imagine there are many.
However I will expand on this a bit for both the “tease” and “torture” aspect.
The tease,
The recipient is being stimulated in a pleasurable manner with what ever device is being used.
The stimulation continues as long as they keep the drainage hose raised up high preventing drainage.
If they lower the hose to allow drainage, the stimulation stops.
When they raise the drainage hose again, the stimulation continues.
So they have a choice, hold/take the enema and enjoy the stimulation or release the enema and not be stimulated. At some point they will have to lower the drainage hose, most can only take 2-3 quarts comfortably. Having 2-3 gallons on hand ensures the cycle will repeat several times before you run out of enema.
The torture,
In this case, both options are unpleasant.
The stimulation is of an unpleasant nature.
The correlation between the height of the drainage hose and the stimulation is reversed.
If they lower the hose allowing drainage, they get the unpleasant stimulation.
If they raise the hose, they have to take/hold the enema.
Again they have a choice, however both options are unpleasant.
The fact that the recipient controls the height of the drainage hose and therefor the level of stimulation adds a mental aspect as the tease/torture isn't just being done to them. They have to make a choice to some extent.