I assume you're talking about a 123 300D. If so there is a valve near the back, I think it is the third one from the rear that is somewhere between extremely difficult and impossible without the wrenches. Even with the wrenches that one is tough. I bought my wrench set for less than $65 but it's been so long ago, I don't remember where.

The wrench set is worth the money though.

My $0.02,