I don't know about this pump specifically, but I used the 1250 on reactors quite a bit and always plumbed them with PVC. So I can tell you how i did it on those; maybe the 1262 is similar. As far as the output goes, if you remove the hose barb you'll see there's an o-ring on it, which means that the female threads in the pump body are not meant to seal; that's what the o-ring is for. There should be some male threads on the outside base of the hose barb with the barb in place. (Usually there's a plastic ring on those threads which you remove) You can get a PVC threaded bushing on those, then attach your threaded female coupler to that; that leaves you with female PVC threads for your plumbing. So you leave the hose barb in place and set up your PVC conections outside of it. Make sense?

The input is trickier. What I did was remove the hose barb from the "cap" that fits into the pump and holds the impeller in place. To do that, you remove the cap (There are some plastic parts which hold it in place) then you can screw out the hose barb. At that point you can get a PVC nipple in the female threads of the cap; use teflon tape and you must get it in there tight while the cap is out and the impeller is not held in place. Then you attach one side of a union to the nipple, again while the whole thing is out. Once that stuff is on and tight, you can replace the cap, installing the impeller. You might have to leave off the silver plastic "guard" that covers that part of the pump. Since the cap spins sort of freely on the plastic clips that hold it onto the pump body, you have to put that side of the PVC union on first. Okay, once it's all together, you have half a union sticking out the the input of the pump and you can attach your plumbing with the other half of the union. On the output side, you have female threads in the coupler above the area of the hose barb (the barb is still installed inside the coupler) so you put a PVC nipple in there and a union on it. Finished!