I think I know what causes the Engine Check light to come on

I got a 98 Camry.

It was on for a while, then on an especially rainy day I rolled into a giant pool of water and heard it spalsh everywhere under my car. Check engine came off at the next red light so I thought dirty sensor.

Couple days later I fill up with gas and when I hop back in check engine is back on. Came off couple days later during a rainy day.

Didn't light on again until today I stopped at a red light in a steep uphill slope and it came back on right there when I started moving forward up the hill.

Basically it's been on and off for the last couple weeks mostly coming on when I put gas in.

I think there's a sensor near the gas cap, where exactly is it located?
Could it be because of gas reflux from the tank when the car pulls from a dead stop?

Is there anything else I could check? I know it's safe to drive but it's annoying as hell.

On an unrelated note : Some motherf*$%er stole my gold emblems, if I find your ass I'll slam my foot right up in it.

Ugh no.
Go get the code<s> scanned. Anyplace will do it for free. Find the nearest auto-parts store.

Otherwise you're either going to troubleshoot randomly until you randomly fix something by luck, or you're going to pay out the ass for somebody to take you for "the ride" until they've felt you've "ridden enough".

autozone will scan it for free

Do you make sure you click the gas cap about three times before starting your car back up? Next time, turn it until you hear it click three times and see if it turns off and stays off. It takes a few drive cycles sometimes to detect that a problem has been fixed if it is not cleared from the computer. You should definitely go get the code read if that doesn't work. My old Camry's light came on periodically for things like the EGR valve and the fuel running too lean.