Basically, the terms of clothing/outfits are on their website.
You can wear anything as ling it is kinky enough. Regular underwear like CK is considered NOT kinky enough. Also, t-shirts, jeans and other normal streetwear is NOT kinky either.
There is a detailed outfit inspection at the entrance after the changing room section.
When I go there, I usually wear Speedos or swim jammers and a harness. Mostly in combination with a puppy hood. I never had any problems regarding admission. My friends neither.
Many people have some kind of kinky clubwear, hotpants, jockstrap, rubber, latex, PVC, etc.
Few are military, Police, Squad style.
Also few leather.