Purl decreasing

My sweater pattern makes a belt casing in the following manor.
[kfb in each stitch across], then 4 rows of [k1 sl 1 wyif across to the end], The decrease calls for [P2tog across] however, it messes up the stockinette pattern in the front because the left stitch lays over the right on the knit side. I need the right to lay over the left on the knit side. Can someone help me?

If you want a left leaning dec to show on the front, then do a ssp - slip 2 sts separately knitwise, put them back on the left needle and purl them together through the back loop. The p2tog dec would be doing the same thing as k2tog on the front and it shouldn’t mess up the stockinette pattern any more than ssp will.

Not sure I understand slipping knitwise. Do you mean I slip the stitches with the right needle going into the stitch from the left to the right? instead of just slipping them onto the right needle?

A purl 2 together through the back loop (p2togtbl) will also give you a left leaning dec on the right side.

Yup, you got it! You insert the needle as if you were going to knit the stitch, but instead, you slip it to the right needle without knitting (or purling) it.

Hope that helps!

Slip the stitch as if you were going to knit it, even on the purl side.

The p2togtbl will also show as a twisted stitch on the knit side, which would disrupt the stockinette even more than a plain p2tog. By doing a ssp, slipping the sts turns them so when you ptbl they lay flat. It’s like the difference between ssk and k2togtbl.

That’s funny, when I do the p2togtbl, (like the video on the Glossary page) the sts don’t twist. The right st lies on top of the left and the slant is to the left.

Yes, the right stitch is supposed to be on the top and slanting to the left - that’s not the ‘twist’ I mean. The individual sts are twisted like when you work tbl. That’s why a ssk isn’t twisted but a k2tog tbl is. Unless you knit combined or eastern style.