Well, I guess you need to find a place that's fairly secluded and near a river. If you're in the river and someone sees you, you can always say, "it's summer, I needed to cool off".
As others have noted, being near a body of water helps. Even using a watery mud pit can get a substantial amount of thicker mud off.
Beyond that, the key to success is 3 gallons of water, a trash bag or two, a sponge, a towel, and some cover clothes. Cover clothes are clothes that cover 90% of you, like a sweatshirt and sweatpants, which you don't mind getting a little bit dirty on the inside.
I once went to a mud bog event where they had a couple acres of the best pudding-consistency mud you've ever seen in your life, and really didn't care what people did in or around it. After watching the trucks for the morning I ended up basically swimming in it and getting head-to-toe covered, letting it dry, jumping back in, you name it. There was no readily-available water source so I had to use just the kit above, which I had in my car. I managed to clean up and check into a hotel without attracting any undue suspicion.
The first key is to strip off your muddy clothes as best you can and put them in the trash bag. This is not the time for modesty. As long as your bits are covered (wear some non-cotton underwear) nobody cares. From there, start removing the mud with the water and the sponge. The key here is *top down*. Always start with the head and work your way down - it conserves water and gets you clean faster since the runoff from cleaning up your head washes off mud further down. Even fully covered in mud with no rinse, I've been able to get de-mudded with 3 gallons of water. If you have a rinse-off body of water or muddy puddle you can probably do it with 1 or 2. Don't forget your back - a lot of mud can hide there and it can be hard to get off. Remember to wash inside your shorts if possible.
Get as much mud off as you can. If you're not wearing a lot of clothes, you'll dry relatively quickly and some residual mud turns into dust or sand which can be brushed off with the towel. Dry dirt is relatively easy to get off compared to mud.
Wrap the towel around yourself and remove any remaining muddy/wet clothes, then put anything muddy or wet into the trash bags. Double-bag if possible, just in case you get a small leak in one bag - you don't want a big wet/muddy spot in your trunk. Getting all the muddy clothes put away before getting re-dressed is important so you don't accidentally splash mud on your cover clothes. Once that's done, put on your dry clothes. As tempting as it is, never put on jeans over wet underwear or socks; the jeans will wick up all the moisture. Quick-dry clothes (like trackpants) are best if you have them. Key final areas to check for mud at this point are the back of your neck and in your ears, particularly the little folds in your ears. Dampen and run your fingers around them or use wet wipes.
You're ready to head home / to your hotel / whatever now, and you'll pass all but a very, very close inspection.
At this point, you should get in the shower when you can. Get in the shower first, then remove your cover clothes in the shower, since any little bits of sand/mud/rocks will fall in the tub and are easily collected or washed down. Shower thoroughly; shampoo helps get all the little rocks and grit out of your hair. Remember to get under your arms well too; mud hides there easily.
If you want to wash your dirty clothes, rinse off as much mud as you can from them in the sink or tub, then stick them back in the trash bags (or a bucket, if you have one) for transport to the washing machine. Here, extra detergent doesn't matter that much since you're not removing oils, you're removing dirt. Your real best friend is the "extra rinse" button on the washer. Add a couple extra rinses to the load, and that will wash off most of the dust/sand particles.
Shoes are a bit of a different story - you have to hand-rinse these. Use a dish-scrubbing brush to get the insides. You can't really use the washer/dryer. Even a fancy dryer with a rack won't usually dry sneakers quickly, the best way to dry those is to leave them outside on a patio for 12-24 hours. Inside doesn't have the same sun/air circulation and doesn't work that well. Almost all shoes except those made completely of rubber (flip flops, some sandals) will absorb water and stay damp for a long time unless they're left out to dry. Including, ironically, water shoes. One of the fastest ways to dry shoes, if you have the chance, is to change into dry cotton socks and wear the wet shoes walking around for an hour or two. Between the socks and the moving, the shoes will dry out a good 80% (and then you can wash the socks).
Throw your stuff (sans shoes) in the dryer - that'll likely dislodge some final small rocks and sand, which is caught by the lint filter or just accumulates in the bottom of the drum. Use a wet paper towel to get that out.
At that point, all the evidence is gone - you're golden and ready for the next adventure. Good luck!
I usually try and find places near my house or near a camping location so I can clean up.
I use to do it during the day but there just seems to be way to many people around no matter how remote you think the location is. Ive been caught a few times
I had a strong desire to get really muddy whilst wearing my work clothes, and couldn't think of a way to do it without the risk of being seen. I wanted to just leave work and get down and dirty as soon as possible! In the end I made an area of mud in the garden, before going to work, and excitedly looked forward to going into it all day. I appreciate this isn't an option for everyone, but it was a lovely safe, private way to have a squelch in mud. I was able to be more relaxed than being in a public place, for example I took my shoes off in the house, preferring to slide into the mud in my socks. It was a lovely feeling strolling up the garden in my socked feet and smart trousers, knowing what was coming!
Several years ago, I went down to a river about 5 minutes from my home. It is not a large river, and on its bank, a company bought about 20 acres, and over the course of a year, turned it into a lettuce farm. But while they were putting in the drainage ditches, containment ponds, etc, there were a lot of muddy places to play. I went there one morning ready for some fun. I had extra cloths, towel, washcloth, etc to get clean. I walked around and looked for some good places walked in the containment ponds, getting down and dirty. I was just getting ready to leave, gotten out of all my clothes, and was getting clean, when a truck drove up to the gate about 300' avay. I was in a depression so the couldn't see me. I hid while watching them. Two men got out and were walking about, looking at the work being done. When they went in a different direction and ran for the river. I didn't get to far when they turned back. Again I hid, and they started walking right to where I was. I crawled into a bush the best I could that was about 20' from the river. I had all my stuff with me in front of me, and hid as best as I could, but my ass and legs were clearly sticking out. They were getting closer, and I could hear them talking about drains and other things, when one of the men said to the other "look, someone had been walking around in the mud" as they could see my foot prints. They then walked closer looking at the drainage going back into the river. This put him about five feet from where I was. Another few feet, and he would have seen my muddy, hairy ass sticking out of the bush. My heart stopped beating and I stopped breathing. He stood there talking about five minutes, then thankfully they turned and walked further on. After about 20 minutes, they were far enough away not to see me, so I made a dash to my truck, buck naked, covered in dry mud, carrying my stuff. I jumped in, and high tailed it home. I was so close to getting caught, and to this day, I don't know what I would have said to them if they saw me. I've never been back there.
Some 20-30 years ago I lived in a house that bordered a swamp on two sides. Being a life-long wammer I of course spent a lot of time exploring that swamp, sometimes while just innocently dumping yard waste, and others while exploring for good muddy areas while fully turned on.
As it happened there was a really nice muddy spot not far into the swamp (within reach of a long hose). The mud had a very high clay content, which of course is ideal for mud play. The area was not perfect, i.e. it contained some rocks, sticks, weeds, etc, so I spent many, many hours out in that mud pit with my wellies, rubber gloves, and a shovel, hoe, and pick axe, getting rid of all of the intrusive stuff. I also used the hoe and pick axe to loosen the bottom soil making the mud pit as deep as possible.
After many weeks of this labor of love I had a mud pit that was nearly circular, about 10 yards in diameter, and at least 1 to 2 feet deep everywhere with nice smooth clay. A long hose leading from the outside spigot to the mud pit could be used to add water to the pit (although being a swamp it never really dried up) but also could be used for cleaning off after getting rather muddy.
After doing all of this, I regrettably did not have many true play times. However, there was one very memorable time when I enlisted the help of my GF (might have been on my birthday, not sure). We went out to the mud pit and she tied my hands securely behind my back and then gave me commands that she picked randomly from a large homemade 6-sided dice. The 6 commands (I'm looking at that dice now) were: Walk Around, Crawl Face Down, Crawl Face Up, Fall Face First, Roll Around, and Bury Head. We went through all of the commands many times while I spent about a hour in the mud pit. It turned out that the seemingly innocent command "Walk Around" was difficult to do without falling down since my hands were tied behind my back and it's not easy to walk in deep mud, and indeed it did result in a few face plants. Needless to say I was totally covered in mud, head to toe, and absolutely loving it!!
Try going at night; Fewer people walking about- so less likely to get caught. You can more easily hide in darkness. Added bonus of having the sun warming up the mud all day first.
Did this in the Isle of Wright- found a lovely mud hole just above the beach. Small layer of water on the top, and deep thick mud under it. Climbing down to it in the dark was ...interesting. As was finding my clothes after. Sliding into that warm pool in the cool night air? Pretty damn awesome.
There are some of the best mudpits in the world near San Antonio but it takes a lot of luck and skill to avoid getting caught, but ultimately, all you can do is minimize your risk, the risk of getting caught is the price you pay for good mudpits as most are at quarries. Message me if you'd like to know more...