I run both chem hoses with my pressure hose. I use elctricial tape to every few feet to keep them together, no snags as I get with zip ties etc... Both chem lines run into a 1/4 inch "3 -way tee" also known as a "2-way ball valve" (must be attached on gun trigger gaurd) one on each side and the middle line goes into the chem injector that is put on after the gun. The valve on the 2- way lets you switch between chems with one finger, put it in the middle and no chems, all while running under pressure. ( I use an open gun for longer pump life)
This is probably not the most attractive setup but you could cover all three lines if wanted. It does add a little weight to the hose lines and gun,if you have hose reels it takes up more space and you would need to get bigger ones ( 300' for 100' of hose). I have found 100' feet to be sufficent for fleets as I can park right among them. I unhhok the setup and use plain longer hoses for other jobs unless I need chems.
Do most injectors not work under pressure? Maybe I came across a type that most don't have? The only downside to this setup is you are putting acid on high pressure,( unless you wanted to use a rollover) although this does not bother me I think it does bother others, although I don't understand why. This system lets me work fast and unecumbered by dragging extra equipment around. I hope this helps a little let me know if you would like pics or more help. I just didn't have any pics of setup in my cpu.