"Clean it every so often. I'd say every 3rd time you go to switch on the compressor"
"Clean it every so often. I'd say, every 3rd time you got to switch on the compressor"
I heard this in a tutorial video on Youtube, a guy talking about when to clean the air compressor.
not a teacher
"Every so often' is common usage, totally acceptable, particularly when it's used in speech, as in this example. Means now and then, occasionally.
Ever so often... doesn't work. It means clean it a lot, all the time.
You can leave out go to or got to and it doesn't change the meaning.
"Clean it every so often. I'd say every 3rd time you (go to) switch on the compressor"
"Clean it every so often. I'd say, every 3rd time you (got to) switch on the compressor"
Third is more formal than 3rd. However, the tone is informal with the "I'd say" so either one is okay.
I'm not a teacher, but I write for a living. Please don't ask me about 2nd conditionals, but I'm a safe bet for what reads well in (American) English.