This is how I clean the bench seats on my trucks. It seems like a huge deal, but not really. Pulling the bench out only takes 10 -30 minutes (depending on your seat belt situation). And allows for a good cleaning. Much better than just spraying some stuff on the fabric and rubbing it in:
1. Release the four seat frame mounting bolts
2. Find an assistant and slide the entire seat out of the truck
3. Use a shop-vac to thoroughly extract as much sand/dirt as you can from the seat
4. Hook up a garden hose and pre-soak the fabric
5. Using a good liquid laundry detergent and a variety of scrub brushes, shampoo the upholstery
6. When the cloth is clean, rinse the detergent away.
7. Keep rinsing until you have rinsed all the detergent (along with the stuff that caused the stains) away. This is step critical - any residual detergent will actually attract soils.
8. Blot dry with lots of clean towels
9. Reinstall the bench in the truck and keep the seat covered with clean towels for a couple of days - until the cloth is dry.
10. When the cloth is completely dry apply Scotchgard Auto Interior Fabric Protector.
BTW - while the bench is out of the truck - and the hose is hooked up - you have a perfect opportunity to blast away all the grime and grit that has accumulated on the slide rails. When clean, re-lubricate with white lithum spray-on grease.