Hello Byron366, welcome and let me see if I can help. I was in your situation five years ago with our in-ground pool. Don’t get me wrong, there is nothing simpler or more economical that the BBB method of maintaining my pool water chemistry. But after two seasons I was really getting tired of feeding my pool 6% bleach from Walmart two to three times per day. It was really taking away from my other fun. So I did some research and found a company called Chem-Tech (I believe they are now called Nova-Tech) on the Web. I purchased one of their XP Series Peristaltic Pumps, along with their 15 gal. chemical holding tank. I believe at the time I spend approximately $450 for the whole thing. (Pump, lines and tank). It’s been the best pool investment I have ever made. I fill the tank with 15 gal. of 12.5% bleach and dial in the dosage and I never have to manually add bleach to the pool. It’s not a fancy sophisticated self checking/monitoring system, so I still have to check the water chemistry, but once I get the dosage dialed in I only have to check the water chemistry every two or three days and adjust accordingly for sun exposure and bather loads. It has made all the difference in the world. I don’t feel like a babysitter to my pool anymore. The injection line from the pump is a ¼” plastic tube that fits into a compression fitting on the injector. The injector gets screwed into a threaded hole in the 2” PVC return line to the pool. This connection point occurs after the heater and all other devices/pumps. I didn’t read in your post where you mentioned the make/model of the automatic chlorinator you purchased, but the injector on my unit is no bigger that ¼” in diameter and only protrudes ½” to ¾” into the 2” PVC return pipe. I have never notice any changes in pressure. Honestly I can’t see how the injector would cause any back pressure or restriction. I have no experience working with flexible PVC other than flexible outdoor conduit, so I can’t speak to the best method of attaching your chlorinator injector or its attachment method. But I don’t believe I would try and drill and tap a hole in the stuff. I’m wondering if a guy could go from flexible PVC to rigid SCH 40 PVC and then back to flexible and drill and tap the necessary hole in the rigid SCH 40 PVC. One thing you want to keep in mind, in my installation the injector HAS to be in the flow of water. You’ll want to check the installation instructions with your chlorinator injection pump. I hope this is helpful. Good luck and if you need more information this forum is a great resource.