Coming into the match on the back of away defeats to Bayonne and Grenoble, Stade need a win to get their season back on track - a situation Papé readily accepts.
He said: "After an opening win we haven't even taken a point from our away trips to Bayonne and Grenoble despite that being our objective. It's a big disappointment.
"Even if there is a lot of waste, I think we have improved compared to last season.
"There's no need to overdo it but we have to take at least four points from the game against Castres.
"They have been in the play-offs for several season now and reached the semi-finals last year.
"Castres have some good players and always recruit well. I think about people like Christophe Samson and Brice Dulin. For me they are genuine contenders for the title so we have to be wary.
"We needed the telling off we got after our defeat to Grenoble. We watched the video back, we could have gone for a drink together but the squad were very professional. "We know we didn't play well and didn't deserve to have a drink, just as we didn't deserve to win."