electric outlet at gas main

I bought a 30 yr old house 2 months ago. The seller said there were never any water pressure problems in the past, other than an occasional waterlogged pressure tank every few years, which took a plumber a few minutes to fix. (He didn’t know what procedure the plumber used.) Starting suddenly last week, I have lots of air coming out of all faucets and toilets in the house. Sometimes it is all air and no water for several seconds at a time, then the water blasts out under VERY high pressure for a few seconds, then resumes normal flow for several seconds or minutes before sometimes repeating this process. There does not appear to be a predictable pattern to it, but in general, all faucets emit air first, then water, when first turned on in the morning. The problem occurs with both hot and cold water. My well is 280’ deep. The pump is 3-4 yrs old. There is black plastic, which I have not inspected yet, running from the pump to the house. There is a 42 gallon galvanized (captive air?) tank. I looked at the pressure gauge on the tank a few times, and it was between 36 and 41 PSI. I don’t know what is “normal” or what the range is supposed to be. I see there is a schrader valve on the inlet side of the pressure tank, but no other valves that I can see. I tried pumping some air into that valve with a bicycle pump, but it didn’t seem to do anything at all. The bike pump read a constant 18 PSI no matter how much I pumped in there. But I am not 100% certain of the accuracy of the bike pump’s pressure gauge. How do I diagnose and fix this problem?

Can someone guide me as to the best connection/fitting combo for this ? P-Trap with copper-to-drain line.