How public is a beach? Well, it depends on the population density, the proximity of overlooking houses, the possibility that one of thise houses has a resident with a telescope, etc. I have done beach enemas using sea water many times with great enjoyment.
I go for a long walk in late afternoon, wearing nothing by speedos and a shirt. Among the beach rubbish I can often pick up a 2 litre milk jug. Rinsing this by filling 1/4 full with coarse sand and topping up to a litre with sea water, I shake it thoroughly and empty on the beach. As dusk draws on, I saunter down to the water again, find a fairly calm spot by some rocks and fill the jug. I stroll with it to a hollow in the primary sand dune and squat over the jug, just pulling my speedos to one side and settling the mouth of the jug on my anus. Then I bear down, both by sitting and with my abdomen as in taking a crap. The water is forced into me as the jug crumples until I am sitting right on the sand. Then I get up, stroll down to the water and risne again (in case there was some blow back!) befor blowing into the jug to uncrumple it (mostly). I then refill the jug with more sea water. can repeat this twice more, each time taking on board about a litre and a half, so that I have a little over four and a half litres in me.
It is now dark enough for me to take off the speedos without much risk. I can see approaching fishermen when their figures are just a blur (as I am to them) and retire into the dunes until they are past. Then I play a game: how far can I walk before I can't hold it any longer? Sea water is irritant and hypertonic, so a good cleaning out is on its way! The best I have managed is four hundred paces! To expel it is only necessary to stop and let go and scrape some sand over what comes crashing out! Sure, my legs get a bit mucky, but a step into the waves, or just wading the river I have to cross before I get home takes care of that. Since 4 1/2 litres is enough to get to the caecum, I probably have to stop four times on my walk, and the last, miost satisfying expulsion of the casecum contents is also usually the greatest volume.
Once home, there will be repeat or two in the toilet; and when I am finished, I have expelled well over five litres. It feels delightfully naughty, and I love being nude in the wind!
Johnny