I've been working with technical fabrics for 15+ years, and as the state health code prohibits me working on non-laundered garments, I've learned a lot over the years....
Techwash, Nikwax or Grangers ( my favorite) are specifically formulated for waterproof breathables, with a toss in the dryer. You can use powdered detergent if you don't have the above, but not liquid
putting jackets in the dryer at a moderate temp will help to reactivate the DWR ( durable water repellency) but the DWR does need to be reapplied every so often, no matter what brand or how much you paid. If water is soaking through your jacket, it's time to reapply. You can also touch up with an iron to reactivate DWR.
A too hot dryer can cause all sorts of problems from delamination of the face membrane or seam tape, to actually melting zippers.
Grime - according to GORE, you can use Shout and other products on grease and grime. I've also used a mild Simple Green solution, but YMMV. If you've got a white coat with grease on it, don't expect perfection. The best way to prevent nasty grime at the collar and cuffs is regular launderings. We do our coats twice a season, and I retreat them in the spring before I put them away.
Wetting out (surface fabric soaking through in rain) is a sure sign that your DWR needs to be reapplied.
Soap flakes is no longer recommended. Some of us are old enough to remember that. Also, dry cleaning is not recommended but if you must do it ask for a clear rinse.
I run into people who think they'll damage it by washing it. You damage it more with a build up of grime, body oil, sweat, dirt and all the other fun stuff that accumulates with use. Ever seen a 15 year old parka that's never been washed? Ew. The DWR is going to wear off no matter what over time - it depends more on environmental conditions than laundering. In fact, not washing
regularlywill cause something called "masking", which causes it to not perform properly
Do not use fabric softeners with technical fabrics. It clogs up the wicking properties and many coats have a wicking liner these days.
People will complain their goretex leaks in the rain. It's probably not leaking. More likely, condensation is building up on the inside. Goretex and similar fabrics are designed to work in cold, drier conditions; not wet humid one. Those billions of microscopic pores can only move so much vapor - if it's really wet out, or you are perspiring heavily, you are overtaxing the ability of the fabric to function and you will be wet.
Goretex and similar DO wear out.
Really good FAQ on washing this stuff here
https://www.grangersusa.com/faq.html