The key is (as many of you have said) to make sure the machine is clean of fabric softener nasties etc and make sure you wash with Tech Wash first. I have heard a lot of people just use TX direct after using regular detergent or not washing at all and simply sticking in the machine with TX direct.
It’s not just the DWR on the outside failing that makes you get wet. If you don’t wash the grime out of it, the dirt impacts the breathability meaning you get wet from the inside.
I’d recommend Re-proofing after every 3 or so washes. Should be no need to reproof after your first wash unless you’ve knackered the jacket already by leaving it too long etc.
Also, I’d recommend the wash-in re-proofer. It generally tends to work better as it ensures you get it everywhere. But I know many prefer the spray as it feels like you can see where it’s going…
Heat activation isn’t really necessary for the aftercare treatments but if the jacket uses PFCs (which most still do) then it will benefit From a blast in the dryer. But be careful as too much heat could delaminate.