Gleet is a fungal infection in chickens that causes a messy vent area with white yucky looking stuff and sticky feathers around their butts.
I'm sure it's not fun for the chickens and ALL my hens had it pretty bad. Feeling it had to be related to something wrong with their nutrition, I let them all go free range. This seemed to help a little but didn't cure it. I kept looking.

An article from the UK suggested giving them vinegar in their water and a digestive probiotic supplement. Also bathing them and applying a topical fungal fighting cream to the area.

I didn't want to put the vinegar in their water because I refresh and give them clean water often and toss the old water on the ground. I didn't want vinegar killing the vegetation. A shout out to the person on here who always asks "would YOU drink out of it" I can't get that out of my head - ever - and ALL the animals' water - including the horses' - is always really clean now including troughs, bowls and buckets. When my husband took care of the animals for a week, I told this to him and now he can't get it out of his head either. And everyone's water was really nice when I got back.

Anyhow - back to conquering the Gleet.

For a flock of 3-4 birds I put 2oz of Apple Cider Vinegar (with the mother) in their food and then mixed in a scoop (the scoop that comes with the bag) of the probiotic. I did this daily. The probiotic brand was

UltraCruz® Poultry Probiotic Supplement for Chickens from San Juan Ranch


I did not do the baths or the fungal cream mainly due to being pretty busy.

The chickens really like this mix and eat it.

It's not a quick fix but keep doing it. Took about 9-10 months of being consistent with it daily.
When they started to molt, the yucky white stuff was falling off in clumps with the feathers.
The new feathers came in nice and fluffy.

A huge win for a vexing problem.