Moliere, you should be able to find everything you need online. We are talking about docusate sodium liquid solution 50 mg/5ml. There are various generic versions of it available from the online medical supply stores. This is the same formulation as the old Colace liquid that was once available in the laxative aisle of most pharmacies. I have not been able to find it in a retail brick and mortar store for years, though.
Up until about 20 years ago, the Colace liquid packaging actually had dosing instructions for both oral and enema administration. That is how I learned that it could be added to an enema. Enema dosage was 5 to 10 ml added to one quart of warm water. I typically used 10 ml added to 2 quarts. After I could no longer find Colace liquid in pharmacies, I stopped using it until I found the generic version online a couple of years ago.
10 mL in 1 quart is easily doable, but only 100mg of docusate. I guess I can try that out and see what happens, but all the recipes I've seen have been 2+ grams per liter, which works out to a much less doable 200mL of docusate solution per quart/liter. 100mL would also be one of the capsules, snip and squeeze becomes much easier with only a few.
I think the Colace should continue to work quite well for your constipation. When I am seriously backed up (5 days or more), I use 10 ml of docusate sodium in an enema and get an amazing cleanout. I actually think it is more effective than a strong soapsuds solution. I can completely evacuate in 15-20 minutes as opposed to 30 minutes plus for plain tap water. Plus, it has a very pronounced softening effect - something you appreciate if you are actually suffering from constipation. I do have some residual cramping later in the day which maybe from irritation of the colon lining. I am not sure that I would use the Colace for purely recreational enemas.
You are definitely right about the docusate, at least at 5mg/2L. It's a "go in and get things done" enema and works very well for that. As recreational enema, probably not unless you're seeking cramps and a big urge. With a retention device, a stern partner, and a timer it could be a very effective punishment enema. Mine was wanting out big-time within 5 minutes, and I was more than happy to let it leave.
I guess what I experienced later on could be called cramping, though I experienced it more as grumbly and active bowels. It went away over the next hour or two and didn't cause a problem with doing what I needed to. I imagine a lower dose of docusate would be even fewer effects.