OK, I am going to say absolutely DO NOT use soap and water on your hole. Using soap will cause micro-cuts in the flesh in and around your hole that will cause very uncomfortable problems later on down the line. Trust me. I am speaking from experience on this. If you're going to go for rimming, use your shower head, hot water, and your hand, and the actual process of cleaning yourself out will take care of the rest.
Anyway, if you're going to attempt penetrative sex, I would honestly recommend reading this guide. It's got some good tips for cleaning yourself out safely: https://www.sfaf.org/collections/beta/anal-douching-safety-tips/
Once you've read that guide, a few additional tips:
As for where to buy the equipment, saline enemas can be purchased from your local pharmacy. I personally use a shower shot, which I purchased from Amazon for about 30 bucks. It requires a little setup, but it's seriously not much hassle to install, all you need is a vice grip wrench and some plumber's thread sealing tape. It does require being careful, but I find it's generally a lot faster at cleaning yourself out thoroughly, and frankly it can feel very good in of itself, whereas the hard-plastic narrow nozzles that regular enemas use can make me sore afterwards.
Next, and this is important: Use the bathroom before you try to clean yourself out. Trust me. If you don't, you're going to regret it and there is going to be a huge, huge mess.
When it comes to actually cleaning yourself out, there are two general approaches. The first is to fill yourself up in the tub, and then squat over the toilet to let it out. This CAN BE overall cleaner, but puts you at risk of an embarrassing accident happening while you're walking from tub to toilet. If your shower is right next to the toilet I say at least try this method. The second method is to just stay in the shower and let it all out there, flushing anything that comes out down the drain with your shower head. This method is a lot easier and a lot faster, and avoids any embarrassing cleanups on the bathroom floor. You'll want to keep some bleach-based cleaner handy that you can use to disinfect the bathtub after you're done, however, and if you're short-sighted enough to need glasses you'll want to bend down and maybe even get on your hands and knees to make sure you haven't missed any detritus and it's all washed down the drain. (Speaking from personal experience here.)
If you opt for a shower shot:
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Watch the pressure! I cannot stress how bad an idea it is to go full-pressure with a shower shot, you will injure yourself permanently if you are not careful. Generally speaking, the recommendation is that if you hold the shot straight up the water shouldn't travel more than 6-12 inches or so.
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Be careful with how long you fill yourself up. If you fill yourself up too much, water is going to escape from your colon into your lower intestine. You can tell if this happened by a cramp followed by a sudden flood of... brownian motion... so to speak. To be clear, this can be desirable since it provides a very deep clean that's great if you're going to be waiting a long while before playing (e.g. 4-12 hours) or if you're going to be experimenting with, say... elbow-deep penetration (which... you won't, since this is your first time...) but most of the time it's a hassle that makes a 5-10 minute process take 30-60 minutes instead, or end up with you canceling altogether and telling your partner it's oral only tonight.
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To avoid the deep-clean above, when you fill yourself up with the shower shot, start by pressing just the tip inside with the water flowing, count to 3 (one-onethousand, two-onethousand, three-onethousand), then take it out and empty yourself. Repeat the process a little deeper, and a little longer, but don't go above a count of 5 or 6.
Finally, if you're unsure whether there's any water left over, lay on your left side in the tub--that points the colon downwards and helps any "leftovers" escape. Once you've finished, you'll be cleaned out for a while--generally speaking, with a normal clean-out you're good for 1-4 hours, and with a deep clean like I described above, you'll be good for about 6-12 hours, roughly speaking.