Old trench coat is probably dry clean only.

If something can’t be washed, it can be for a variety of reasons. The agitation could damage something, the dyes might not be set and risk bleeding, shoulderpads could soak up tons of water for a long time … usually one of those three. Maybe a few others I’m missing for weirder stuff.

If you don’t want to do that, you can try hand washing it in a bathtub. Test a small area first, see if dye runs or anything. If it’s fine, then just wash it gently, kinda get your medieval peasant on. Then you can wring out any shoulderpads or anything, and hang it up with good ventilation to dry. Should be fine. Probably.

I’m no expert but I think it’s wash on cold and dry with low heat for delicates. If your coat is valuable tho I’d suggest taking it to a professional cleaner or even a basic dry cleaner.

A good rule of thumb: If it’s outerwear meant to protect you from the elements, it’s probably best to dry clean.

Anything valuable/formal should be dry cleaned.

But most semi-formal, business-type clothes, casual night out clothes, even if fancy in appearance can be machine washed with cold water, especially with newer more gentle washing machines & detergents.

The dryer is a different story and it’s a good idea to just never dry anything on high heat at all ever unless you’re literally trying to kill something (by disinfecting it lol). Even t-shirts last longer when dried on low heat.

if it’s wool, have it dry cleaned

if it’s leather, use equal parts vinegar & water