I have used butt plugs in the past with the largest diameter being
1 3/4 inches (could never get a 2" diameter one in- too painful). With the 1 3/4" one I found that my sphincter was loose for a few days and a big urge to have a BM resulted in incontinence. Sometimes when getting some colonic urging the plug would try to override the sphincter come out. Pushing it back up would relieve the urge to push it out and defecate, making me think that when the narrow part is well seated through the sphincter, there is less of an urge to expel. The heavier metal ones I would think would follow the law of gravity with the wider part more likely to press against the sphincter and inducing the sensation of needing to defecate.
Wearing a well fitting thong helps as it provides counter pressure upwardly against the flange of the plug. Also, the flange on the plastic ones is too big and would begin to hurt the perineal skin. A smaller oval or rounded flange would be more comfortable and still be big enough to not lose the plug into the rectum. I have used glycerin suppositories in the evening to evacuate my rectum before inserting my butt plug but if left in overnight I would start having the uncontrollable urge to have a BM before morning and removing a soiled plug in the middle of the night is not fun.
I still use suppositories before going to bed to evacuate my rectum but use a douche nozzle covered with a condom. There is enough of a the wider tip to prevent it from completely passing the sphincter and into the rectum, plus most of the good feeling is due to any type of insertable being in the sphincter canal. The feeling is still wonderful; it even slides up and down a little giving more pleasurable friction than a shorter necked plug and I don't get the "urge" so I can leave it in until morning and take a shower immediately after removing it and having my morning BM.
Being of the age where erections are more challenging, the anal sensation of the douche nozzle in place helps a lot. Wearing a thong with the thin strap over the nozzle helps holds it in place to keep it from sliding out and I can still have sex with the wife by pulling the pouch to the side but with the anal strap still in place over the tip of the nozzle. Lubrication for me was not a big problem - inside the rectum there are mucous glands that provide lubrication so probably only a little KY or vaseline applied around the outside without needing to remove the plug should be enough to avoid the dryness. I would like to hear other comments about the use of and pleasure of butt plugs.