The largest object I ever used was a cucumber fresh picked from the garden. It was still warm from the sun and after washing the dirt off it felt so nice that I wanted to take it inside me. So I took off my clothing, and pushed the cucumber against my vagina. (I intended it to go in my butt but I needed some natural lube). It took some pushing, but I pretended the guy had a really huge penis and I just had to take it in me. I also pretended I was giving birth, which I know is weird. After I pushed it in as deep as I could, there were still several inches sticking out, which made it look like I had a fat green penis. I played around for a while, standing up and walking around with this thing sticking out of me. But finally I decided to pull and push it out, which took some effort. But it was all lubed up and so I moved to my rear.
That took much longer and was more difficult, trying to get my anus to open. But it was also fun. I finally managed to get it to partially enter with some pain, but I was somehow driven to do it. As I continued pushing I felt it filling me inside. Finally I had this awesome feeling from my anus closing as the cucumber disappeared inside me. But I was also apprehensive because it was totally inside me and unlike with my vagina, there was nothing sticking out to grab on to in order to pull it out. While it was inside I played around and finally had an orgasm. After that I wanted the cucumber out of me, and so I pushed, and pushed. I could feel the cucumber pressing and causing my anus to partially open, but when I stopped pushing it went back in. I imagined myself giving birth where the baby is too big to come out. I kept pushing as hard as I could and felt my anus open wider but still not enough to allow the cucumber to come out. Plus it hurt. Finally I stopped pushing, deciding to leave it inside for now. Surprisingly it did not hurt being inside although it made me feel full. Later I tried again, pushing as hard as I could, with the same result, unable to get it out. But then I had the idea to try a new technique, stretching my butt hole from the outside, which required another cucumber about the same diameter. So I picked one from the garden, thankfully we had lots of cucumbers, and used Vaseline to lube both my anus and the cucumber. Then I began to push it in to stretch my anus. It also felt weird with the new cucumber bumping against the one inside. With the new cucumber about half way in, I began to push it out and hopefully the one inside as well. It was painful with my anus being forced to stretch so wide, and felt so good when it closed as the second cucumber popped back out. But I could not stop or else the first cucumber would still be stuck inside. So I pushed as hard as I could and even though it was painful to feel my anus stretching, I kept pushing and felt the cucumber emerging and soon experienced the most wonderful relief and pleasure as my anus closed with the cucumber now outside. I was sore for the next few days.
Sorry for this being so long but I am not good at summarizing experiences so I wrote the whole thing.