@TheChoccoBiccy good morning dear.
I have almost the same kink, except for my toys going past the sigmoid, without means of retrieval. I do colon depth play, anal stretching and i like to insert toys in my rectum past the anal sphincter, fully inserted.
To answer your question, first of all I'm not a medical person just a horny anal self player in bed. So you will have to make your own conclusions in what you are going for.
Anyway dear i have the experience of up to 3 pool balls inside at one time. That's as far as i am going without any form of retrieval, and only when I'm extra horny and thinking like “oh what the heck, one more ball”
I have inserted bigger items like a baseball or an apple, even a buttplug with the base cut off (especially for the purpose of going all the way in) and lately I'm even inserting a small buttplug with the base inside me.
For the next explanation I'm referring to a 2¼ inch pool ball, since i think they are the safest. (What is safety right 😃 )
Anyway, my experience is that once a toy reaches a certain depth it becomes a little stuck (trapped 😃 ) inside the prolapse. I can sometimes push to get it out while laying in bed, sometimes i stand up and push or walk a little before I push.
And sometimes i just can't get the pool ball out of my prolapse. I have made a “tool” out of a garden table/footrest and placed a toilet seat on it with the opening cut out of the table. So if i have one stuck i sit down on the toilet seat, and up until now, I'm able to push it out. This is because of the toilet seat position your internal plumbing and open your cheeks.
How deep before it gets stuck? That varies from time to time as well as positions. If i lay down sometimes ball number 2 gets stuck, if I'm on my knees and insert them upwards i can usually have all 3. It also depends on the amount of lube i have inside and whether i have opened up before with large stretching toys.
Also important is not to get scared or freaked out, stay relaxed, that helps your sphincter.
So here you have my 2 cents.
PS my anal comfortable sizes are 3.2 inch diameter and approx 19 inch deep, so I'm not a beginner.
Also, after reading your question again, i have done up to 5 hard boiled peeled eggs at one time, with the last one taking it's time to get out, but it did. I have also put a couple if mandarins inside me with no issues, except when i decided to peel them first, but the acid gave a bit of not so pleasant sensation, so i pushed them out quickly.
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