Holy crap! A 175 would throw that rug around like an evangelist handing out collection plates. CRB would be a better choice.Poly shag, one of the worst rugs to clean. You want to use a high pH prespray, boosted with ammonia, scrub with a 175, rinse with a garden hose, extract with an extremely hot truck mount and then just throw it away cause it's not going to get any better.
A 175 with a shampoo brush won't be a problem. We use a 175 on most of our rugs, even floppy rugs.Holy crap! A 175 would throw that rug around like an evangelist handing out collection plates. CRB would be a better choice.