Danny D:
No, the way I read that Lasco article, you should not be using EITHER pipe dope OR teflon tape on plastic pipe threads.
You should be using a thread sealant meant for plastic threads ONLY. The Lasco article really should come out and say that pipe dope is not the same thing as thread sealant meant for plastic threads. It dances around that point by saying that pipe dope hardens whereas thread sealant for plastic pipe threads doesn't, thereby allowing it to be pushed into leakage paths by the water pressure inside the pipe, thereby blocking that leakage path. It also says that pipe dope and teflon make the threads slippery, thereby reducing friction and causing overtightening, whereas a thread sealant meant for plastic threads won't do that.
Putting the thread sealant on the male threads, then wrapping them with teflon tape is just as bad as using teflon tape only. The thickness of the teflon tape you put on is going to increase the spreading force on the female fitting making it more likely to split.
From my reading of that Lasco article, you should apply thread sealant meant for plastic threads to your male plastic threads only, and then screw on the female plastic thread. Tighten to finger tight and then no more than two full turns after that.
If you've already used teflon tape on your threaded plastic joints, and there's no splitting or leaking, I would just leave them as is. But, in future, just use the red bottle that says it's meant for plastic and nothing else.
I think everyone in here understands the principle of tapered threads, and that the idea behind teflon tape or pipe dope is that these materials get compressed between the make and female threads to seal the joint against leakage. That Lasco article said that metal threads can gall at metal-to-metal contact points, and that the use of teflon tape or pipe dope helps to prevent that. In the case of a smooth plastic-to-plastic thread contact, there's no risk of galling so you don't need anything as thick as pipe dope or teflon tape to keep the metals separated until the joint is fully tightened. With plastic theads, all that's needed to seal the tightened joint is a fluid that's viscous enough not to be pushed out of the joint by the water pressure inside the pipe. I'm thinking that plastic fittings can be molded to much better tolerances than iron pipe can be machined (because the cutting tool wears down for one thing), so a fluid that's fairly thin may still be viscous enough to not be pushed out of a small enough crevice in a threaded joint. Or, at least, at the lower water pressures that plastic piping is suitable for. So, even if this thread sealant you bought for plastic piping seems to be too thin compared to pipe dope, I would still use it by itself, which is what Lasko is telling you to do.