I’m a novice, but what worked for us was soaking our bird, and gently taking the feces off. The chicken needs to be relaxed and not stimulated to strain at all. Here is the whole story:
Naomi, our beloved 6 month old leghorn, had a prolapsed vent. As a new chicken mama (mama of 8- 2 each-leghorn, australorp, rhode island red, ericana/Americana), I didn’t know what to do, so of course I took her to the vet and received the bad news that this was often the beginning of the end. I watched the vet clean off her bottom with the sprayer/faucet. The vet’s advice: keep her clean, warm, isolated and push the prolapse back in when it came out again and put sugar on the prolapse to reduce swelling. We did more and less than that. She took over our laundry room, so was isolated and warm; however, every time I cleaned her, she strained so hard that she would prolapse even further. I swear that she pushed her entire insides out by several inches. And when I pushed the prolapse back, she seemed to be hurt, even vomited once, and I kept forgetting the sugar. So, after feeling guilty for hurting her and balling at dinner (yes, I was balling over my girl), I gave up keeping her clean and gave up pushing the prolapse back. My husband and I were desperate. We were considering relocating her to the family farm to live out her days as a free range chicken, but we knew that had negatives as well, when my brilliant husband suggested a hot tub. No, not for us, but he wondered if soaking the poop off without stimulating her to push would be helpful, so we filled the kitchen sink with warm water and I added a little shampoo. I held her body under the water for a few minutes. I leaned over her so she wouldn’t be able to struggle and when I removed the feces, it peeled right off, easy peasy. Since my hand was on her bottom, I felt the vent go back inside. Naomi didn’t strain at all. I took her out of the sink and wrapped her in towels and held her for a while so she could dry (I liked the snuggling part too). Then I left her wrapped loosely in the towels, placed her back in the laundry room in a bin (with the lid off). In the morning, I found her right where I left her, but something was different: her bottom feathers were beginning to fluff out again, and best of all, no prolapse! No feces on her bottom and no prolapse! We released her later that day and she is now at the bottom of the pecking order, poor thing, but still, a month later, no prolapse. I believe she has only laid one egg since, which is great! We want her to heal and not lay eggs for a while.