Let me give you the tips and tricks I picked up from backpacking:

- Never use liquid detergent on waterproof fabrics, unless it's a special wash just for them.*
- Wash waterproof fabrics on gentle cycle, cold/cold.
- Don't put waterproof fabrics through the dryer. (see exception below)

*Nikwak Tech Wash or other special designed liquid detergent for DWR/GTX fabrics.

If the dirt isn't coming out, then just deal. It's probably set in the fabric and stained there for good. Don't wash it in high heat or with the wrong soap because that will destroy the coating on the fabric, ruining the waterproof quality.
DWR coated fabrics can sometimes be revived with dry heat. A quick (10 min) gentle tumble in a medium heat clothes dryer, or a light ironing on low settings may work. If neither solution revives the water repellency, then bring out the big guns and use something like Nikwax Wash-In Waterproofing.