A lot of this is personal process but as has been said the bottom will already have a lot of prep work so that it really is like deep kissing. Generally you won't taste much (once you get beyond the toothpaste/mouth wash). Your tongue starts out slow and then ventures further and further into your partners mouth. Passion sets the stage of how long and deep the kissing will go. I think this is much the same. My tongue doesn't immediately push into the hole. There is kissing and licking the outside and then a small amount of the tongue will go in. I will listen to my partner to make sure he is enjoying it. That is what I meant by appreciative moaning. Then I just work my tongue in more and more. Of course, I will take time out to kiss and lick the outside and then go back in and try to go deeper. I may use a finger if my tongue is removed and see if he (my partner) likes that. Some will move back and forth on my finger. Then I might pull my partner's cheeks apart which allows even further access. One thing I have learned is that a lot of saliva helps in sliding deeper and deeper. I happen to be blessed in producing an inordinate amount (my dentist has commented on it ) so I use that. And then at a certain point I ask my partner to press his face down into the bed so that he is stable enough to reach back and pull his cheeks far apart. That gets me even further into him. Of course, there are other tricks such as if you have stubble you can rub against the hole during the rimming. Some guys like it, some guys don't. I like at some point to get my partner to push his butt further into the air so that I can pull his hard (hopefully) cock back toward my mouth so that I can suck him a while. After blowing him for a bit, I will go back to rimming and then alternate. So it really is your technique and what you get to know about the guy you are with. As your chief concern was cleanliness, well it is next to godliness and a prerequisite. However there is a lot to gain from it.