I though I'd pass this tip along since I've used this product at least twice in the past so many years.
Once a year, I give my Aerostich Roadcrafter II a thorough wash. I might as well since I can't ride during the winter months.
If your suit is black or grey, chances are you won't see what dirt is ground into the textile material, but mine is red and the dirt is visibly ground-in, in numerous areas.
Instead of using higher priced products like NikWax Tech-Wash, I've been using Shout Stain Remover. A large 946 ml squeeze bottle goes for $2.43 at Wal-Mart and will do a whole suit.
I don't use a washing machine because it tends to be a bit hard on the 3M reflective material and suit in general. I'll apply the Shout to the whole suit in sections and lightly brush it in. After an hour or more, I'll let it soak for at least two hours in a laundry tub of hot water with Tide (that by itself, never got my suit clean). After hand agitation in the laundy tub and many thorough rinsings, the spin cycle of the washing machine is used to semi-dry the suit before hanging it up to air dry.
I also noticed that the Shout was a lot gentler on colors than the laundry detergents I've used previously.
I've been using 3M Outdoor Scotchguard to waterproof my suits since 1992.
According to some sources (maybe some with vested interests), detergent should not be used on Gore-Tex fabrics unless they are very thoroughly rinsed. I believe that I read in the Aerostich catalog that the suit should be dryed in a dryer to "re-activate" the pores in the Gore-Tex material. In any case, my Aerostich keeps me dry in some pretty heavy downpours for a given time, beyond that, I'll use a rainsuit over it.