How to clean boat canvas of normal dirt, not near salt water.?

Answer 1

There is a foam product sold at car supply stores that do a great job. I just had it done. Sorry that I cannot recall the name but it comes in a can and works great.

Answer 2

I just take mine (22 foot) to LaundryMat and use the biggest commercial Front loader machine they have. I use one half the soap of whatever the machine calls for. If you live in Florida (alot of rain) then you will need to scotch-guard it after 2 or 3 washes.
Don't use dryers, just put it back on boat, damp - Let the sun do its thang... Leave a flap open so air can circulate.